CHAPTER 3 - (Part 1)

301. Kant came onto the philosophical scene at a time when modern philosophy had already made some headway.
He combined a thoroughly analytical mind with a profound study of previous philosophers; to some extent he opposed them all; to some extent he also agreed with them all.
Nevertheless, the outward form of his eclecticism was so original in its expression and so regular in its form that it seemed a new system, perfectly coherent and wonderfully put together.
The spirit of his age, by which he was thoroughly influenced, tended towards Locke whose philosophy had undergone various changes and met hostility from various quarters. Kant went along with his age and took a further step in the same direction.

302. In commencing this brief, obligatory exposé of his system, I wish to point out that he adhered without prior investigation to Locke's principle that all our cognitions are derived from experience [App., no. 27]. 'However,' he adds, 'if all our cognitions come from our experience, it is necessary for us: 1. to investigate the nature and various species of our cognitions; 2. to see how experience can transmit all cognitions to us.'
In this he was correct: Locke had begun by explaining the origin of our cognitions. This was a departure from the sound method in philosophy, a hasty pursuit of cause before getting to know and examine facts. The facts were human cognitions which Locke should first have examined carefully. He should have obtained an intimate knowledge of their nature, analysed them, pointed out their constituent elements, classified them and sorted them into all their species. Explaining the origins of human cognitions amounts to assigning them a cause proportioned to their nature, from which they are derived or may be derived. However, before a suitable, proportioned cause can be assigned, we first need to address the issue of the qualities and parts of the effect without which the inquiry cannot begin. As a result of this procedural error, Locke, instead of beginning his inquiry at the natural starting point, plunged 'in half-way'. He attempted the impossible, that is, to explain what he did not yet know because he had failed to examine it.

303. In attacking Locke from this quarter, Kant adopted Leibniz's approach.
Leibniz had challenged Locke on the issue of the faculties of the spirit; Kant challenged Locke on the issue of the cognitions produced by these faculties. Both argued in the same way. Leibniz had stated: I am willing to agree that, in attributing to the human spirit a reflective faculty over and above sensitivity, all human cognitions are explicable. The whole issue consists in seeing whether this reflective faculty can exist without being endowed with innate concepts. Kant said to Locke: I am willing to concede that all human cognitions come from experience. The whole issue consists in seeing whether experience, which produces all the knowledge we have, is possible if it furnishes the spirit with sensations alone.

Kant was pointing out that it is one thing to say: 'All our cognitions come from experience' and another to say: 'All our cognitions come from the senses.'(224)
There is no doubt, he says, that we have no knowledge at all before we have any experience, that is, before we make use of our faculties. But does this mean that our experience is obtained purely through our sensitivity? This is a quite different question; in order to answer it, we need to know what the fruit of our experience is (cognitions), and to see whether this fruit can be the product of sensitivity alone.

304. The first task to be undertaken by any philosopher is the investigation of the different species of human knowledge; the second, assuming that they all derive from experience, is to inquire into the conditions necessary for such experience(225) to provide us with all the different types of cognitions which we have identified. I shall examine both tasks.
Prior to Kant, all philosophers without exception had realised and accepted as an obvious fact that our cognitions are of two kinds. They distinguished them by calling them a priori and a posteriori cognitions. This distinction we owe to the Scholastic philosophers, who took it from the ancients. We can say, therefore, that it has the support of every age.

305. Let us confine ourselves to showing that it is accepted by modern philosophers who are otherwise deeply divided.
Descartes accepted a priori knowledge and in it alone found the source of certitude. Locke recognises the distinction to which I am referring. He writes:

Note his immediate conclusion:

It seems impossible that, having noted the universality of some of our ideas and noted also the impossibility of finding this universality outside our spirit, he did not subsequently perceive the need to accept that our spirit needs something other than that provided by the senses. But at times, although we are no further from the truth than a hairsbreadth, we cannot bridge that tiny gap.(228)

In his Cours d'Etudes, Condillac asserts that this distinction between a priori and experimental truths really exists. From the former, he derives rational evidence and from the latter, evidence of feeling and factual evidence.
Leibniz agrees and also proves that the certainty of our cognitions cannot be derived in any way from sensations, but from the mind itself.
Thus, all conflicting philosophical schools seem equally to recognise as a fact that our knowledge is of two species. We can, therefore, take this as a sure starting point enabling progress to be achieved in this field.

306. The characteristics of a priori knowledge specified by Leibniz and Kant(230) are necessity and universality. The experience of our senses shows us what is but cannot show us what must be. There is absolutely no necessary reason to say that a fact which happens once, twice or a hundred times in one way, must also happen in the same way on the hundred and first time. If, therefore, sense experience gives us knowledge of things which happen, such knowledge is not necessary. Knowledge of some contingent thing is always a posteriori. On the other hand, necessary knowledge may be a priori. Indeed, its necessity never comes from the senses but from an intrinsic reason seen by the mind. This seems so obvious that it cannot be doubted.(231)

Each morning we see the sun rise and we predict that the sun will rise the following day, but this is a mere conjecture based on analogy for which we can offer no intrinsic reason. In fact, there is nothing repugnant in our imagining that the sun will not rise tomorrow. God can indeed halt it in mid-course. On the other hand, to say, 'The part can be greater than the whole', is so repugnant that no one could possibly admit it as true. This is not because we have never seen a part greater than a whole, but because we feel it to be an intellectual impossibility. If we are talking of something which we have never experienced, we can say at most that we do not know whether it will happen or how it will happen. However, from the mere fact that we have never seen it happen, we do not say that it is impossible because, to say this, we have to find an intrinsic, logical repugnance to the thing.

A posteriori knowledge, then, such as that of sensible facts, is accidental knowledge. In addition to such knowledge, there is within us necessary knowledge which is called a priori precisely because it has as its basis an intrinsic necessity bestowed by pure reason, not in any way by the senses.
Sense experience, as well as offering us knowledge devoid of necessity, also offers us knowledge devoid of universality.

We can have experience only of a determined number of cases. If we wish to find out whether all jasmines are equally sweet-smelling, we can go into the garden, and pick one, two, three, ten, twenty, fifty flowers. If we are patient enough to smell them one by one, but do not wish to venture beyond the knowledge given us by experience, we can only learn from these tests that one, two, three, ten, twenty or fifty flowers have transmitted the same sweet, distinct fragrance to us. Further than that we cannot go. Any advance beyond this by our mind goes beyond the limits of experience.
We cannot even say from experience that the flowers we have picked, when brought up to our nose once again, will give off the same scent. We say they will, but only by a law of analogy which, when applied, enables our mind to transcend the narrow limits of its experience.

If, after the fifty tests, we see that the flowers left on the pergola are similar in everything to those we have picked and smelt, and we imagine and conjecture that these too, when sniffed, would transmit the same pleasant scent, we go far beyond the limits of experience, and are in fact pushing the analogy much further. A similarity proved valid by tests upon fifty flowers is applied to thousands of untried flowers. In other words, from the jasmines which we have smelt, we argue that all other jasmines even outside the garden have the same scent. In our imagination, we run through all the other gardens and all plants of the same flower in bloom throughout the world, and apply to all of them the result of our little experiment.

Nor does the mind stop here; it transcends the bounds of experience(232) much more freely because the mind also thinks of all possible jasmines and applies and attributes the same fragrance to them all. Books on botany, therefore, rightly assign the fragrance to the species of plants called jasmines.

Thus, it is clear that knowledge derived purely from sensible experience is not and can never be universal. It is only particular, and more or less extended according to my opportunity and occasion for acquiring it. It is always infinitely restricted, however, when compared to universal knowledge which, to be such, must apply and does apply to all possible examples of a species, which are infinite.

307. The universality of a priori knowledge is due to its necessity.
Indeed, what is necessary must always be what it is. On the other hand, universality obtained by applying, for example, the law of analogy to some observation of mine is not true, rigorous universality. It is merely, to use Kant's expression, 'only an arbitrary extension of validity from that which may be predicated of a proposition valid in most cases to that which is asserted of a proposition which holds good in all.'(233)

308. A point which needs the greatest emphasis is that if we were to focus on the senses alone, we would never be able to furnish our cognitions even with this imperfect universality of analogy.
In fact, if we considered only what the senses give us, we would never have even the thought of any universality whatever.

Let us imagine that we have perceived six objects. We cannot extend our experience with our mind to a seventh object because we have not perceived it. Still less can we extend it to all existent beings, relative to which what we have perceived may be a tiny proportion. And it is even more impossible to extend it to absolutely all possible objects. For this final extension, we must have conceived some universality, that is, the conception of the indefinite possibility of objects which cannot be experienced by the senses because they do not exist, but are solely able to exist.

309. It follows that even this universality by analogy, although not necessary, although uncertain, presupposes in our mind some a priori knowledge which owes nothing to the senses. If necessity is inevitably accompanied by de facto universality, analogy presupposes in us the concept of some potential universality. Necessity, de facto universality, potential universality are concepts which transcend all sense experience and can be explained only by deduction from the inner power of our mind itself [App., no. 28].

310. Locke had laid down the principle, 'All ideas are derived from sensations and from reflection.'
At the same time, he had recognised this fact: 'Human knowledge is of two species, a priori and a posteriori.'
He had not realised that the two propositions were incompatible, and that one must inevitably cancel out the other.
If he had noticed it, he would either have altered his principle: 'All human knowledge is derived from sensation and reflection'(234) or denied the fact that an a priori, necessary, universal knowledge existed, just as he denied the other fact - that we have some notion of substance(235) - because he saw that it was not easily reconcilable with his theory.

311. However, no error concealed in a philosophical theory, no matter how tiny and invisible it may be initially, can remain there for long without beginning to proliferate. Like truth, error is subject to development but, when developed and fully grown, unfolds all its ugliness and harmfulness. There is nothing hidden that will not be revealed. In this case, the revelation of error is a necessary step in overcoming and destroying it, just as tumours on the human body have to swell and burst before the body can regain health.
Hume absorbed Locke's philosophy through his studies; it had become the philosophy of his age. Even the most apparently independent thinkers feel the influence of opinions around them. Hume thus accepted critically, as an established fact handed down by tradition from his teachers, Locke's judgment: 'The only cognitions we have come from the senses.'

Having retained this principle, he began to examine Locke's other proposition, 'A priori knowledge exists,'(236) and saw clearly that it is irreconcilable with the principle admitted by this philosophy.

312. Let us take, said Hume, one of the most famous a priori propositions: 'Every effect must have its cause.' The necessity of this proposition, that every effect must have its cause, cannot in any way be deduced from sense experience for the following reasons.
First, sensible experience presents us with facts alone, each completely distinct from the other. One fact may be observed to follow another repeatedly, constantly, as the feeling of heat succeeds the sensation of light when the sun rises. This, however, is simply a conjunction of two facts, distributed in the order of time. But there is nothing to assure me that they are connected as cause and effect. I cannot say that one fact is the cause of another solely because one comes before the other. It is obvious that the succession of two things gives me no right to consider them as linked together as cause and effect.(237)

Next, let us assume that my senses enable me to perceive the link of cause and effect between two facts (something utterly impossible because the senses provide a mere temporal conjunction). I would still have no right to conclude that the thing had to be so, and could not be otherwise. The senses tell me what is; they cannot tell me what must be and do not therefore provide the necessity expressed in the proposition 'Every effect MUST have its cause'.

Third, if I could note through the senses 1. the causes of a number of facts I have witnessed and 2. that these facts must inevitably have their causes, I would still not know that the thing would always happen in the same way, even in the case of events which I have not experienced, or in the case of all possible facts. The universality exemplified in the proposition: 'Every effect must have its cause', could not be given me in any way by the senses because universality is not experienced; all existing occurrences are not investigated, and possible occurrences, which do not yet exist, do not fall under the senses.(238)
Hume concluded therefore that the proposition, 'Every effect must have its cause', could not be deduced in any way from sense experience.

313. However, the principle: 'All our knowledge had its origin in sensations', was already accepted as irrevocably true; on this point there could be no compromise. All that remained was to apply the method of argument which Locke had used when discussing the idea of substance. This consisted in rejecting as non-existent anything which conflicted with the principle of his system.
The idea of substance, considered to be at odds with this principle, was denied by Locke. In the same way, Hume, having discovered an identical incompatibility (overlooked by Locke) in a priori knowledge, found it necessary to deny that such knowledge existed.
He therefore denied that the principle: 'Every effect must have its cause', was a necessary, universal truth. In a word, he affirmed that this pronouncement of human common sense was unjustified.

314. But why does mankind deceive itself in this way? Why do we always assume the pronouncement to be true, and use it continually in all our reasoning?
Hume put the mistake down to habit. It is so easy to switch from the idea of conjunction to that of connection; it is so easy to consider one item as cause and the other as effect when one constantly precedes and the other constantly follows. It is so easy for us to confuse one thing with another and call cause and effect all regularly succeeding facts. Moreover, if our erroneous judgment were confined to things we actually experienced, there could never be a universal proposition. We arbitrarily render a proposition universal by extrapolating experience beyond its set limits. Having experienced many examples of succession and the apparent interdependence of two facts, we conclude that this will always be the case, even for unexperienced facts, as well as for those non-existent but merely possible facts. We thus invent the universal proposition and believe that 'All effects have a cause.'
But this proposition, rendered universal by the imagination, would still not be necessary. We make our imagination work even harder and perfect the maxim. We imagine that the proposition cannot be otherwise than it is, and that all effects must necessarily have a cause. We then restrict the proposition to this solemn statement: 'All effects must have a cause'.

315. In this way, a necessary, universal proposition, which had always been accepted by the whole of mankind, on which all human reasoning is based, which is the foundation of all the most lofty truths, of all beliefs, of all ethical doctrines, is eliminated from modern philosophy. 'Nothing can happen without a cause' is now viewed as an illusion created by the over-hasty imagination of the whole of humanity. All mankind is convicted of error by Locke's principle that human cognitions have their origin in the senses alone. A few philosophers immediately prior to us rebelled against common sense, which they abandoned to the countless masses and schools. They discovered and proclaimed a theory so simple and profound that, in assigning to sensations alone the right to produce ideas, it declares everything rational to be empty illusion merely because it is not sensible.

316. It is obvious that Hume was under no obligation to stop here; he could have extended much further the consequences of Locke's theory.
The very argument that Hume devised to invalidate the proposition considered by everyone to be obvious, 'Every event must have its cause', can be used to destroy every other axiom. The universal formula to wreak such havoc runs as follows: 'An axiom is a necessary, universal proposition. It cannot be derived from the senses because they do not provide anything necessary and universal. But we have no other knowledge than that which comes to us from the senses. Therefore, we do not possess any axiomata; we cannot be certain of any necessary, universal proposition; in short, our arguments have no fixed principle from which to begin' [App., no. 29].
Consequently, Locke's principle, 'All our knowledge comes from the senses', contradicts the fact, 'A priori knowledge exists'. Anyone, therefore, who accepts Locke's principle and wishes to be consistent, must deny human beings the knowledge of any universal, necessary proposition.

317. But to grasp the implications of denying any kind of universal, necessary proposition, we should note that, if universal, necessary propositions are eliminated, the possibility of any certainty is eliminated and complete scepticism reigns.
First, we have no experience of anything which does not fall under the senses.
If we eliminate universal, necessary propositions, it is obvious that we no longer have any principle from which to deduce non-sensible truths.

Anything not falling under our senses cannot be deduced, by means of a principle, from what falls under our senses. For example, I deduce from geometrical shapes drawn upon a beach that some unseen human being has been there. To do this I rely on the principle: 'No effect occurs without a sufficient cause.' If I eliminate this principle, I am no longer able to deduce from the geometrical shapes the existence of a human being who has drawn them on the sand. All principles are necessary and universal of their nature, otherwise they would not produce necessity in any consequence.
I deduce the existence of other people's souls and the existence of God from their effects by the principle of causality.

Once a priori knowledge is eliminated, together with certainty about everything which does not fall under my senses and the possibility of knowing what does not fall under my senses, only the outward appearances pertaining to the senses remain. The whole world shrinks to a heap of appearances; to myself, I am merely an appearance. The consequence of this reasoning is universal, boundless, sceptical idealism. Such is the inevitable outcome of Locke's principle: 'All our knowledge is derived from the senses.'
Furthermore, even sensible appearances will not endure. I am not even certain of these.

To be certain of anything, I always need a necessary principle; certainty is simply an inevitable necessity to which my intellect yields assent. I cannot possess certainty about simple, sensible phenomena, unless there is a prior, necessary principle in my mind whose authority assures me of their existence.
If I were to say to myself: 'I am certain that I am being modified, that I perceive sensations in my senses,' my reason, reflecting upon my presumption of certainty, would immediately ask: 'And why are you certain that you perceive something?' If I were to reply: 'Because it is impossible not to feel what I am feeling,' my reason would retort: 'This is a universal principle, an a priori principle; it is the principle of contradiction. But who assures you of it? It does not come to you from the senses because the senses do not provide you with anything which contains necessity - as this principle does - or universality with which the principle you have employed is endowed. To trust the senses unfailingly, you must resort to a necessary, universal principle, to an a priori principle, to the principle of contradiction, in short, to reason, to me. The senses need to have their authority guaranteed by reason.'

318. Reason, therefore, does not have its origin in the senses. It needs to be necessary and universal; the senses are particular and contingent. No certainty is forthcoming except by means of a necessary principle not derived from the senses, that is, a principle which cannot be otherwise and is, therefore, universal. Certainty which did not occasion necessity would be very curious. 'I am certain that this is how things are, but they could also be different!' Isn't this a contradiction? Consequently, if we believe rationally in the senses, we must have a reason for believing in them. This reason cannot originate in the senses; if it did, we would lose our way by resorting to reasons ad infinitum.

The destruction of a priori knowledge, therefore, brings with it the destruction of a posteriori knowledge which only exists through the agency of a necessary, universal reason, not originating from the senses. So the principle, 'All human knowledge comes only through the senses', finishes in absolute, universal doubt. But even this is nonsense. There cannot even be doubt without a rational principle, independent of the senses, which constrained us to doubt.(239) The real conclusion is complete and total destruction of everything we know. Not only is it impossible for human beings to be certain; it is impossible for them even to doubt. Reason is an impossibility, and the principle deprives mankind of intelligence, its special prerogative. Either we must deny a fact as luminous as 'Man is a rational ens', or we must abandon the ruinous principle, 'All human knowledge comes from the senses.'(240)

319. These final consequences, which are not drawn even by Hume, are none the less necessary. Once the principle is accepted, we cannot call a halt; all consequences must inexorably follow their course. Its fecundity must be totally exhausted; if it is an erroneous principle, this fecundity finally brings about the destruction of all that is true, of everything that is. Amidst such destruction, the very principle is engulfed and along with it those who proclaim it.

320. Hume denied a fact which Locke accepted: 'There is a priori knowledge', that is, necessary, universal knowledge, because he found that it clashed with Locke's theory, summed up in the following proposition: 'All our cognitions draw their origin from the senses and from reflection upon the operations of the spirit.'
Hume could have been refuted by proving, as all facts are proved, that a priori knowledge exists. Reid and Kant chose to follow this path.
It would, however, have been difficult to persuade a sceptic like Hume, who was deeply prejudiced in favour of his own ideas, that universal and necessary propositions do exist and are not, in fact, figments or suppositions of our imagination.

No matter how often you insist with such a philosopher that these propositions are accepted as absolutely necessary and universal by all mankind, he will probably reply: 'I do not deny that fact which, indeed, I am trying to explain. Rather, I maintain that this fact comes about as the result of a mistake which everyone commits inadvertently, due to the extreme affinity and proximity between ideas of conjunction in time and ideas of connection between cause and effect. Because of their proximity, great care must be exercised in distinguishing them from one another and, up to now, society has been unable to do so. Ordinary people especially, who represent the great majority of mankind, cannot sustain the first idea without slipping into the second. It is extremely difficult for them not to switch from the sensation created by the sun in the different points in the heaven to the belief that the sun moves, although the sensation of motion is different from real motion and is merely apparent. Mankind, therefore, easily confuses appearance and reality, and falls into erroneous judgments. This is what happens in the case of the principle of causality. People take it as necessary and universal, but it is so only in appearance.'

One might have replied that raw experience is totally different from necessity; even when I see the sun rise every day of my life, I do not conceive the contrary as impossible, as I do with the proposition: 'There is no effect without a cause.' Even if the experience were repeated indefinitely, even if I were convinced that it would continue for ever in the same way, I could never be persuaded that the opposite was impossible, unthinkable, an inherent contradiction. Consequently, analysis of contingent propositions obtained from a long, sustained experience and analysis of necessary propositions such as 'There is no effect without a cause' is perfectly adequate to enable us to distinguish between these two series of propositions and avoid any confusion between them. We do not exchange the supposed universality and necessity of the former for the intrinsic universality and necessity with which the latter are clearly endowed.

321. However, a shorter, more convincing approach when refuting philosophers of this kind would be to follow their line of argument and start from what they themselves admit and recognise as undeniable.
The fact which they acknowledge is that all accept the proposition, 'There is no effect without a cause', recognising and using it as necessary and universal. But while admitting this, they deny that the proposition is necessary and universal; they say that it is only apparently so.
If we start from the fact which they admit as true, we could put the following argument to them:
You admit that the proposition, 'Every effect must have a cause', is necessary and universal only in appearance. But I shall prove to you that this could not even appear to be true to human beings unless they had a priori knowledge which is not sense-based, that is, truly necessary, universal knowledge.

Let us assume that the proposition, 'Every effect must have its cause', is merely the limited result of experience and, when strictly formulated, is expressed as follows: 'Certain occurrences repeatedly precede certain others.' My question now is: for human imagination to have been able to transform this empirical proposition into the rational proposition, 'Every effect must have its cause', what concepts do we need? Obviously we could not have been guilty of such a confusion unless we had 1. the idea of possibility; 2. the idea of cause; 3. the idea of necessity; 4. the idea of universality. None of these ideas, however, can be derived from the senses, as even our opponents concede. In other words, it is impossible to have 1. the idea of possibility, because the possibility of a thing does not fall under the senses; 2. the idea of cause, because only effects fall under the senses; 3. the idea of necessity, because the senses show what is, not what must be; 4. the idea of universality, because sense experience is limited to a given number of things and repeated only a given number of times. It follows that the problem we face in accepting the principle of causality as true is also to be faced in accepting it as apparent. If human beings had only sense experience, we could not have formed, or even assumed and imagined, such a principle.

What escaped Hume in this argument is the realisation that we must go beyond the senses, not only to imagine as necessary the axiom, 'Every effect must have its cause', but even simply to imagine it as possible, simply to conceive it. Because Hume did not see this, he grants that mankind only imagines it to be true. But this admission is sufficient to ruin his entire theory. In order to have the idea of something, it is not necessary that it should really subsist. All that is needed is that I should think it. Mankind thinks necessity and universality. Therefore, these ideas are within us whether they are applicable to external things or not. Their origin needs an explanation; the senses do not provide it; consequently, we either deny the principle, 'All ideas come from the senses' or deny not only that the principle of causality is true, but that it is considered as true by anyone. We have to say that it has never been thought by the human mind, never imagined and never spoken of. But how would you rule out a principle without thinking it, without naming it? The sceptical argument based upon the famous axiom, 'All our knowledge comes from the senses', is essentially selfcontradictory.

322. The two propositions accepted by Locke, 'All human knowledge comes from the senses and from reflection devoid of ideas' and 'A priori knowledge, that is, necessary, universal knowledge exists', were incompatible, as we saw, and the former destroyed the latter.
The first proposition was a philosopher's theory; the second was a fact of nature.
This destruction is proof that Locke's theory had run its bitter course. The philosophers who found it at this stage were in a position to assess it. One of these, the Scot, Reid, was in no doubt - as we have already seen (cf. 99, 116) - that the wrong path had been chosen, and that people were being led to absolute nihilism. This is essentially repugnant to human nature and mankind had no option but to retrace its steps.

Reid, unlike Hume, focused on the second proposition and maintained with all the greatest philosophers down the ages that 'a priori knowledge, that is, necessary, universal knowledge, is an undeniable fact; Locke's theory is false because it cannot be reconciled in any way with this luminous fact.'
Having rejected Locke's principle, Reid had to replace it with something that showed how a priori knowledge was possible.
Reid did not concern himself unduly with showing the possibility of a priori knowledge in general. He went no further than explaining how we acquire knowledge of the existence of bodies, which is based upon some elements of a priori knowledge, and which Berkeley and Hume had denied [App., no. 30].

With this in mind, he set about analysing the way in which we form the idea of bodies, and thought he had to distinguish three successive stages in the acquisition of this knowledge: 1. the impression made upon our sense organs by real exterior entities; 2. the sensation which immediately arises in our soul, granted this automatic impression; finally, 3. the perception of the existence and sensible qualities of bodies which occurs in our spirit simultaneously with sensation.

Sensation has no feature making it similar to the outward impression, just as the perception of the existence of bodies has no similarity to sensation. These three things occur in succession; this is the essential fact. One cannot be called the cause of another because all three are entirely different. The reason why these three things occur in succession is beyond our grasp; it is a mystery.

What we can say is that, as sensation cannot be the cause of the perception of the existence of bodies, we must admit in the spirit itself some innate activity or instinct which leads the spirit, immediately after sensation, to judge of the existence of bodies. This instinctive judgment, which is not the effect of sensations (which are simply associated with the judgment chronologically), is responsible for the immediate knowledge or thought in our spirit that bodies are something and exist furnished with certain qualities.

323. Reid considered that his theory had put paid to idealism and scepticism. In fact, he evaded neither, as I shall show.
Idealists and sceptics start from the principle: 'We cannot know anything beyond sensation.' The idealists conclude from this: 'To say, therefore, that bodies exist is a gratuitous affirmation; all that we know to exist are sensations; there cannot be anything other than sensations.' The sceptics, who are more logical, go further and conclude: 'As a result, we have no principle of reasoning which warrants our moving from sensation to the knowledge of anything else, bodily or spiritual.'

Reid mainly had the idealists in his sights. He felt that the destruction of idealism would lead to the collapse of scepticism, and argued as follows: 'It is an undeniable fact that everyone has knowledge of bodies. Such knowledge, which cannot come to us from sensations, must therefore follow from an inner faculty of the spirit, from an instinct which, as soon as sensations arise, ensures that the spirit has an inner perception of bodies.'

However, as soon as he accepts - and, in fact, takes as the basis of his system - that sensation has no connection with the perception of the existence of bodies and that these two things, sensation and perception, are so distinct that they have not the slightest similarity to each other, how can he be sure that the immediate perception of bodies is not a delusion? What assurance is there that the perception of bodily entities corresponds to the entia themselves? This would seem an unjustified assertion, and the arguments about sensations would seem to have the same force when transferred to its perception.

The reason why idealists and sceptics conclude that we cannot be sure of the existence of bodies was this: 'Sensation, which is purely subjective, has no connection with the real existence of bodies. The common view that supposes the existence of bodily substances external to us with their own objective existence, independent of our modifications, is worthless.'
Reid replies: 'Bodies are not perceived through sensations, but through a perception which occurs instantaneously in the spirit when sensations are experienced. Sensations then are quite unlike perception.'

But, granted this, it remains to be proved that this immediate perception of bodies is true. Instead, Reid has sought a better explanation of how the common error originates. According to him, people are driven to perceive bodies through a blind instinct, through a law of their nature. There is no reason pointing them in that direction other than mere, inevitable necessity. Yes, we may reply, it is perfectly obvious that everyone accepts the existence of bodies. By your admission, they cannot do otherwise. Nature, not reason, impels them to do so. Common sense is nothing but blind faith, a universal illusion which mankind passively accepts without knowing what kind of authority presents and imposes it upon us. Reid's system, therefore, does not solve the problem of idealism and scepticism. All that has been done is to set it back one stage. The problem which arose over sensation is transferred to immediate perception. Common sense remains involved in doubt and without authority [App., no. 31].

Reid wished to apply his views on the immediate perception of bodies to principles of reason such as causality. According to him, we perceive them immediately by an inexplicable insight, by a natural instinct which sets them before us and arbitrarily forces us to give them our assent. He succeeded in explaining their origin, but did not succeed in endowing them with any rational authority to which, as human beings, we must bend our free assent.

324. Locke had unwittingly introduced the principle of scepticism into his teaching; it was to burgeon under Hume.
Reid, in his desire to refute Hume's scepticism, which was rooted in Locke's principle, denied the principle but replaced it by another which contained the seed of the disease itself. He planted it deeper, all unknowingly. It was destined to grow, and did in fact grow under Kant's direction.

The fact, 'A priori knowledge exists', which was denied by Hume and vindicated by Reid, was accepted by Kant.
This fact is attested by all mankind. However, common sense, which has the authority to establish such a fact, cannot offer any explanation for it. All say, 'We know necessary, universal propositions', but do not say how they know them, nor explain why they are impelled to give them their assent.
Reid had said: 'This assent, by which all assert necessary, universal propositions is a natural, instinctive judgment which cannot be explained. We must simply affirm it as a mysterious fact.'

As we saw, this meant admitting the existence of a priori knowledge in us, but simultaneously denying its authority and veracity. This was the path Kant chose to follow.

325. Kant's teaching can be summarised as follows.
We have no knowledge prior to experience, but Locke was wrong in asserting that all our knowledge comes from the senses.
Our knowledge is: 1. partly a priori, that is, necessary and universal; 2. partly a posteriori, that is, contingent and particular. We have to explain how experience, which furnishes us with both these cognitions, is possible.
A priori knowledge, that is, necessary, universal knowledge, has no connection with sensations. It arises, therefore, from within us, as Reid says, and develops from the very depth of our spirit on the occasion of sensations.

Nevertheless, we still have to investigate how this last fact, that is, the arousal of a priori knowledge in our spirit on the occasion of sensations, is possible. Reid was content to note the fact, but it must also be analysed. In addition, we have to discover the conditions by which it is determined. This is the point at which Kant's particular contribution begins. He analyses perception in so far as it contains a priori knowledge which Reid had previously accepted but not described in detail nor differentiated according to all its species.

326. Kant set about showing that when sensations occur, the human spirit does actually perceive external entia which, however, are not simply presented to it by sensations. External entia are not, as sensists claim, a cluster of sensations; they are entia, and are made up of two distinct elements, that is, 1. sensations, and 2. qualities posited by the spirit itself. Kant calls these qualities forms, as he had called sensations matter.
It follows that entia of the sensible world, in so far as we perceive them, are made up of matter and form. Matter is provided to us by sense, and consists of everything contingent and particular in these entia; form is provided by the understanding and consists of everything necessary and universal in them. In a word, form posits the a priori element of cognitions, matter posits the a posteriori element.

I perceive a tree and, in doing so, experience not only the sensible modifications of my bodily organs which, as subjective modifications or sensations, posit nothing outside myself, but also admit, with the activity in my understanding, something external to me. This has its own independent existence, independent of me and any modifications in me. According to Kant, in order to be able to accept this tree as external to me, to represent it to myself, and in a word to form it for myself, I must - with the activity of my spirit - add necessary, universal notions to sensation. No solid objection to this proposition can, in fact, be raised because (ignoring the forms of sensitivity, that is, space and time), I have to add at least the universal notion of existence or that of possibility. I have not perceived a tree with my understanding until I have judged that it exists or can exist.

327. Kant set himself to discover and describe with philosophical thoroughness all the universal notions which contribute to the formation of a corporeal ens as conceived. He reduced them to fourteen, two of which he named forms of the external and internal sense. These were space and time. The other twelve he called forms of the intellect or categories, that is, twelve universal ideas into which it is always necessary to locate, as in classes, real, perceived entities. In fact, our understanding, in perceiving what is real, merely places them in one or other of these classes: to perceive something real with our understanding is to classify and judge it.

The four general classes, each of which he sub-divides further into three minor subdivisions, are quantity, quality, relationship and modality.

According to Kant, it is impossible to perceive anything without perceiving it as furnished with a certain quantity and a certain quality, without perceiving some relationship such as substance or accident, and some mode of existence such as contingency or necessity.
Placing something real in these four classes is a necessary condition without which intellectual perception is impossible. This is a condition of experience, the experience through which we acquire our cognitions. Experience is impossible and thinking is impossible, unless we assume that the understanding, in perceiving what is real, carries out such a classification.

But carrying out such classification is the same as judging real things under this fourfold division; judging them is the same as furnishing them with the four predicates of quantity, quality, relationship and modality which, as universals, cannot originate in the senses, but are generated by the understanding in the act of perception. By means of these predicates, real entities acquire their being as objects. These predicates can, therefore, be called the form, and sensation the matter from which results the intellective object.(241)

328. Kant claims to have avoided idealism and scepticism in this way, but he refuted it in one sense only: by stating that Berkeley's idealism and Hume's scepticism were too narrow.
He transferred the idealism of Berkeley from the senses to the understanding itself.
Berkeley had said: 'Bodies have no real existence outside us; they are nothing but our sensations.' This was a consequence of Locke's theory: 'As we possess only sensations, we can only define the idea of bodies, which we have, as a cluster of sensations.'

Kant defines bodies as: 'A union (a synthesis) of intellectual forms and of sensations.'
Both come from us: intellectual forms from the activity of our understanding; sensations from the receptivity of our sense. We know nothing real; we do not even know whether anything real in itself and external to us is possible.
This consequence comes straight from Reid's theory. He had said: 'The bodies which we perceive are not our sensations alone; an instinct of our understanding induces us to add an object to them.' The admission that we perceive this object by a blind operation in our spirit enabled Kant to conclude: 'It is therefore simply a product of our spirit.'
Kant states: 'I am not an idealist, because I do not accept that bodies are mere sensations as Berkeley does.' He accepts the title in a loftier sense, that is, he aims to be a transcendental idealist: this is the same as saying: 'I am not an idealist at Berkeley's level.'(242)

329. Kant also says that he is not a sceptic. According to him, scepticism consists in the rejection of the correspondence between our ideas and entia external to us. He does not reject such a correspondence. He analyses the objects thought by us and finds that they result from two elements, an empirical element (sensations), and a rational element (intellectual concepts). If these two elements do not unite, there is no thought object. But we can speak about thought objects. There are not two things, therefore, the thought object and the concept of the object, about which we may debate whether any correspondence exists. There is only one thing, of which my concept is one part, my sensation the other. Reid said: 'There are only external objects, not ideas of those objects.' If he had been faithful to his principles, he would have said: 'There are no objects which are not ideas.'

To perceive something, says Kant, is the same as saying that my understanding sees it as endowed with a certain quantity, quality, relationship and modality. I could not see it unless I placed it, with a judgment, into these four classes, that is, by assigning to it a quantity, a quality, some relationship at least with itself, and a mode of being.
Now, our understanding could not assign such universal notions without having them within itself. They do not come from the senses. It follows that our understanding of itself partially creates its object. In other words, it gives the object its form; the matter is provided by the senses.
This is really what Kant means when he says:

Elsewhere, he writes:

Consequently, the issue of scepticism is completely banished from critical philosophy because the sceptic asks: 'How can we be sure that entia correspond to the concepts we form of them?' Critical philosophy states: 'Concepts are not actually a representation of entia but part of them, that is, their formal part.'

330. It appears, however, that Kant by offering this justification takes undue advantage of his readers. His apparently serious explanation is his usual way of pulling the wool over peoples' eyes.
Everyone knows, of course, that scepticism consists in denying the certainty of things in themselves, independently of any modifications in our spirit. To reduce scepticism to the question: 'Do perceived entia correspond to our concepts?' is to alter the question.

Kant tells us that we are sure of phenomena only, that the objects of our thought are derived, relative to form, from our limited spirit, that we do not even have the idea of things which exist in themselves and not in us (that is, the ideas of noumena), that we do not know whether things in themselves are possible. In doing so, he involves us in such universal idealism, in such deep, subjective illusion that we are enclosed in a circle of inescapable illusions without hope of attaining reality. Truly, this does not make us unsure of what we know, and cannot therefore be called scepticism, but it does proclaim that we are incapable of any knowledge. Kant, by rendering all true knowledge of real things impossible and absurd, produces a much sadder scepticism than usual. This is perfected scepticism, consummated under the new title, critical philosophy. In this way, mankind itself (which exists purely to know) is eliminated and the work of modern philosophy is fulfilled.

Kant himself admits that criticism is an essentially negative teaching, but compares philosophy before his time to the rash, impossible venture of the Tower of Babel. The human spirit lies humiliated in the dust. This is the final outcome of its wisdom. After centuries of meditation, of delusion and self-congratulation as it proceeded arrogantly to conquer truth, it comes to the end of its journey, when it hoped to gather in the abundant harvest of its labours, and concludes by admitting its own impotence and nothingness. And it prides itself upon this as its greatest and ultimate discovery!

331. The basic error in critical philosophy lies in its having made the objects of thought subjective.
These objects are the result of sensations (matter) and of intellective forms. Sensations are modifications of our feeling and, according to Kant, are insufficient to constitute an argument for believing in the existence of an external cause that may have produced them. To be able to draw such a conclusion, one would have to accept the efficacy of the principle of causae.

However, the principle of cause and all the other forms, which do not originate in sensations, emanate from our spirit. They do so, Kant says, precisely because they do not come from sensations. Kant finds nothing midway between the origination of knowledge or some of its elements from sensations, and origination from our spirit. However, such an argument by exclusion is patently arbitrary and false because of the imperfect enumeration of possible cases. Such is the fundamental error of this school and the original sin of all the German philosophies which appeared after Kant's and took their direction from him.

The assumption - upon which Kant builds his system and for which he offers not the slightest evidence - that anything within our understanding which is alien to sensations must necessarily originate from the thinking subject, was due to his failure to notice that being has two modes (one subjective, the other objective) and that in both, being is identical.

Being in the objective mode is being which makes itself known, and makes itself known as it is, even when it is subjective. But because being is identical, knowledge is efficacious and true.

External things have subjective existence (to which extrasubjective existence is reduced). If we wish to know them, we must add to them objective existence which is their intelligibility. This objective existence is the part that does not come from sense; the subjective part comes from sense but is not known without objective existence because nothing can be known if it has no intelligibility. However, this does not change things because being is identical in the two modes; it is simply illuminated, it is known.

332. The fact is that we perceive external things, as it were by means of an instrument suitable for the purpose, by the idea of existence. When we form the judgment: 'Such and such a real entity exists', we apply the universal predicate of existence to the particular subject, that is, to the sensible action we experience. However, it does not follow from this that with our activity we introduce universal existence into the thing perceived. We merely find in it its own particular existence and introduce the latter - which we have not created but recognised - into universal existence. In other words, we place the thing in the universal class of existing entia; we know them.

If the existence which we perceive in affirming a given real thing were exactly the same as that which we have in our intellect when we perceive a real entity, we would have to introduce into the perceived real thing a universal existence because existence is universal in our intellect. However, this is not the case. We do not introduce a particular existence into a real thing determined to the thing alone. We already see it there because we know its own subjective existence by means of its objective existence.

Kant's failure to distinguish between the prior concept of the mind, which is always universal, and the thing, always particular, conceived by means of this concept, led the author of critical philosophy into another error. He considered that the intellectual concept and the thing corresponding to it were one and the same. For him, the whole universe was a product of human understanding and human sensitivity. The understanding posited the form, and sensitivity the matter as two ingredients required to constitute all the entia of the world. He should have realised that the part contributed by the intellect in knowledge is confined to making known what the thing contains without contributing anything to it. He would have done this if he had considered how the objective form, which is in the mind, restricts itself to the measure of sensible, subjective real things.

333. This observation on the idea of existence must also be made on any other idea and especially on the twelve Kantian categories to which, in Kant's view, all universals are reduced.
To show more clearly the truth of our observation, I shall apply the argument I have expounded to quantity, one of the four main ideas or categories.
The idea of quantity which I have in my mind is not, in fact, a quantity of the same type as that which I perceive with the help of my senses in a material ens, for example, in a house. These are two entirely distinct modes of quantity.

This distinction is obvious. Although the two modes of quantity, that which I have in my mind and that which I perceive in the house, are both designated by a single term, they nevertheless are different in character. The quantity which I have in my mind is characterised by a universality void of any measurement; in the case of the house, I do not, in fact, perceive universal quantity, or possible quantity applicable to other entia, but a determinate, proper and individual quantity of the house itself, indissociable from the house. This quantity is therefore contrary to the idea, as the particular is contrary to the universal, and the ideal to the real. One excludes the other. The quantity which my mind conceives is not exactly that which I perceive by sense in the house, although I know the latter by means of the former. Critical philosophy errs, therefore, when it assumes that in perceiving external entia, we introduce into them the idea of quantity in our mind. The argument used is similar to that of Condillac when he points out that we refer and attribute to bodies the sensation of colour which exists only in ourselves. But regardless of Condillac's argument, that of Kant, which is similar to Condillac's, - although applied to ideas instead of sensations - is seen to be false as soon as the distinction between universal concept and particular attribute is grasped, that is, rendered particular by the sensible determinations proper to the perceived ens.

The same argument must be applied to the idea of quality and that of relationship (I shall deal with modality later on), and to their subordinate ideas, as well as to any idea we may wish to use to judge some real thing by attributing to it the quality expressed by the idea. It will always be necessary to distinguish, between the idea and the real, particular quality in the thing we recognise. The idea is the rule according to which we form our judgment; the particular quality in the external thing which we recognise is the result of our judgment; it is that which we have come to know by means of that judgment. It is not true, therefore, that our intellect inserts its idea as such into the thing, although it uses its idea to know what is in the felt thing when it is understood. It places what is felt into its idea and thus makes the external, real thing a true, complete object of cognition.(244)

334. The truth of this distinction appears even more clearly when we consider what we do in pronouncing a judgment upon things, when we say, for example, 'This house is large.'
Let us analyse the statement. It contains nothing indicating that we have built the house, it says nothing about any size we have given the house. The meaning of the words presents simply an operation of our spirit with which it recognises the size of the house.
If we look more closely at this operation, we see that it assumes the idea of size which we use to recognise the real size of the house. The idea of size, therefore, is not the size of the house, because one is ideal and the other real. The ideal size is an instrument, as it were, by which we know the real size. Particular, real sizes are infinite; ideal, universal size is one and immutable.

Common sense bears witness to this. The whole of mankind, all the schools, ordinary folk everywhere have distinguished between the idea of a quality and the quality subsisting in a thing. They acknowledged that the idea can be present in our mind even when the subsistent quality does not exist. Kant, when accepting a priori knowledge, that is, necessary, universal knowledge, started from common sense and said to Locke: 'The existence of such knowledge is undeniable because people everywhere accept it'. Can he not admit now that the distinction of which I am speaking - between the idea of a quality and the particular quality shared by things - is also affirmed by common sense.(245) Kant, who devised a theory to explain a fact posited by common sense, also has to make room in the theory for other facts which relate to the same issue and are equally attested to and posited by human common sense.

Finally, if there were no true difference between my idea and the corresponding part of the house, I would be unable to tell one from another. In this case, why has everyone made the distinction? What is the basis of such a distinction? This is the ideological question.

(224) Kant does not always appear consistent in his evaluation of experience. When he says: 'All our knowledge begins with experience, but not all our knowledge is derived from experience' (Critique of Pure Reason, Introduction 1), he uses the word experience relative to our senses. On the other hand, when he asks: 'How is experience possible?' (ibid., 2), he seems to be using experience as the source of all our cognitions, and to distinguish it from the senses. In this case, he takes the word experience to mean the acts of our spirit, which are a combination of sensitivity and intelligence. As a rule, however, he attributes the first meaning to the word experience. For myself, I prefer to use it in the second way because I think that this brings out better the essential core of Kant's thinking. In doing this, I am straying somewhat from his habitual mode of expression, but not from the substance of his philosophy. I warn my readers of this so that they can, if necessary, make adjustments to the terms I use.

(225) As a rule, modern philosophers accept that all human knowledge comes from experience but without asking what experience is.Is experience perhaps facts? Facts alone cannot constitute experience because until facts are known by me they are, relative to my knowledge, non-existent.Nor can experience be taken to mean facts known to me. If this is the meaning of experience, we would have to inquire about the kind of knowledge under discussion. It would be absurd to maintain that experience is facts known by sense alone. When I say that I know a fact by sense alone, I have removed all thought from the fact. In such a case, facts are sensations and nothing more; there is no contact between them, no connection of any kind. These facts known by the senses alone - an incorrect expression if ever there was one - can neither be written or spoken about, because language does not have individual words suitable to express them and because, if I connect them to some sensible sign to make them speakable, I would have to reflect upon them. But this runs counter to the assumption that they are known to me through sense alone, and nothing else.Experience, therefore, will be facts which are truly known; this inevitably brings in the intelligence which endows them with some universality by considering individual facts in relationship to being and, in being, in their relation to one another. Thus they form classes or species. This kind of experience can and does produce our cognitions. But if this is the experience we mean when we assert that all our cognitions come from experience, we first have to discover the nature of our intellective knowledge of facts and the nature of the intellect which we use to form or, at least, complete this experience. We also have to examine how such a faculty of knowledge must be constituted to be capable of having such experience. In other words, we want to know if this faculty has anything innate, and if so, what. This again amounts to discovering the conditions which make such experience possible.

(226) Locke uses the word essence, but in other passages maintains that we have not the slightest knowledge of essence. This is the eternal contradiction to be faced by all philosophers determined to banish from the field of human knowledge something which mankind cannot forego. They specifically exclude something as foreign to philosophical inquiry but later introduce it indirectly and unknowingly into their arguments and presuppose what they previously had stubbornly rejected. They have to do so; otherwise they could not argue or converse. Essences of things are elements in all human thinking; discourse, which is based upon the first principles of common sense, is mainly reduced to the expression of essences. It is impossible to speak without expressing essences or alluding to them.

(227) Bk. 4, c. 3.

(228) Locke says: 'The only place for universal ideas is in our spirit, and it is reflection which furnishes the mind with them.' But how does reflection furnish the mind with them? 'By abstraction,' replies Locke, 'to which it subjects the particular ideas derived from the senses.' But what does abstraction do? It divides up, it breaks down; it does not add or create anything. He assumes, therefore, that a component, a common, universal concept is present as an element in particular ideas. The origin of this universal concept, therefore, still requires an explanation. When particular ideas are formed in this manner, Locke's abstraction intervenes and breaks them down into their elements. It discovers what is abstract and what is sensible. It reconstitutes them and unites them in as many ways as it wants. But unless this intellectual perception is granted, Locke's reflection has nothing on which to operate.

(229) Kant took care to define exactly the meaning of this phrase, a priori knowledge, in order to avoid equivocations in the development of the argument.He points out that this term is used in two senses:

Kant uses the term, 'a priori knowledge' solely in this second sense.

(230) Other philosophers saw this but, among modern thinkers, these two focused more specifically upon certain characteristics and sensed their importance. The achievements of great philosophers are almost always confined to this: metaphysical truths are known but are not differentiated and defined in a way that brings out their great fecundity. These ideas do not take their rightful place in the genealogical table of ideas, in the human spirit, and in the appraisal made of them.

(231) Even the sceptical Hume accepts that truths which consist of relations between ideas are necessary.

(232) Our experience of anything whatsoever, however many times it is repeated, is slight, even infinitely slight in relation to all possible cases. It is almost nothing in relationship to a universal, necessary idea which encompasses whatever is possible.

(233) Critique of Pure Reason, Introduction 2. When we render universal a particular proposition that has come to us through sensible experience, we cannot truly be certain of this universality. Let us examine experientially a part of the human body. The dissection of countless corpses offers us the following result; the liver is connected to the right part of the heart. Next, let us attempt to universalise this fact repeatedly demonstrated to us by experience by stating: 'All human bodies have the heart on the left and the liver on the right.' But we cannot be absolutely certain of the truth of such a statement because it does not possess any intrinsic necessity. Unknown to me there may be cases where the opposite is true. On the contrary, independently of experience, I can know that I have to doubt it. Experience may confirm my doubt; thus, during a dissection of a body carried out in Paris, Leibniz relates that the heart was located on the right and the liver on the left.However, to avoid any ambiguities, I should point out that when I universalise experience, I conceive the result of it as either accidental or essential to the thing. It is essential when the result relates to what shapes and constitutes the substantial concept of the thing. For example, the statement: 'Man is a being endowed with reason' is a proposition which expresses the essence of man. When, therefore, I experience it, I accept it as necessary in so far as I form the concept of man only by means of the rational element which intervenes to form him. Consequently, I could no longer conceive him without the use of reason. Hypothetically, therefore, every man must possess reason. Without it, he would not be what I call man. Thus, necessity and universality are founded in the knowledge of essences and Locke is, yet again, in self-contradiction when he acknowledges a truly universal knowledge and denies that we know the essences of things. However, knowledge of essences is not given to us by the sense experience of which we have spoken.

(234) Locke defines reflection as the application of our attention to sensations and to the other operations of our spirit. Consequently, it merely adverts to what the spirit already has within it. This is his error. If Locke had posited reflection without defining it, he could have saved himself by approaching it from its more favourable side, as Leibniz tried to do.

(235) We have already seen that the problem of deducing the idea of substance from sensations arises from the idea of existence contained in the idea of substance. But the idea of existence is the idea of something more common than anything else. Thus, the difficulty present in explaining the origin of substance through deduction from the senses, is the same as that present in trying to deduce universal or common ideas from them. Moreover, it is universal ideas, particularly those of essence and substance, which produce necessity in propositions, as I have already remarked (cf. 305). But Locke, giving no thought to this, denied the idea of substance because it seemed to clash with his principle of the origin of ideas and, at the same time, recognised the existence of necessary and universal notions and of a priori knowledge. He did not see that the very same problem arises when we seek to explain the origin of the latter.

(236) Actually, he investigated this proposition only in part, and discussed only a single part of a priori knowledge, that is, the principle of causation. If he had been consistent, he would have saved nothing. His argument would have demolished a priori knowledge completely, down to the last fragment.

(237) Any fact pertaining to outward experience is merely an effect; the cause does not fall under the external senses.

(238) In expounding Hume's thought, I am reinforcing it with reasons which are perhaps even more powerful than his own; but the core of the argument is the same.

(239) Doubt always implies some certainty because it is a negation of certainty. Doubt and certainty are relative ideas: the former cannot be conceived without the latter. To say, 'I doubt', is to affirm something. In order to rule out certainty and affirmation completely, we should need to cease thinking. The very act of negation would contain an affirmation, because the act with which we deny cannot be included in the total denial.

(240) Descartes, therefore, is incorrect when he says: 'The senses are simply sources of error.' He ought to have said: 'The senses are sources neither of error, nor of truth, nor of doubt.' On their own, the senses are incapable of producing thought, which is always exhibited under one of these three modes: truth, falsity or doubt. These are modes of thought and not sensations. To say that the senses mislead us is to attribute to them one of the modes of thought. But if the senses were capable of possessing one of the forms of thought, they could also possess all the others. It would be absurd to say that the faculty enabling us to affirm error was different from that enabling us to affirm truth. The senses are not sources of error, as Descartes maintains, nor are they sources of knowledge, as Locke maintains. They produce no knowledge whatsoever, no idea, no truth; they merely furnish our mind with the matter of knowledge with which our mind forms a judgment. To do so, it must inevitably possess some universal idea.

(241) It should not be thought that the distinction between the matter and the form of our cognitions is a discovery of Kant; it is ancient, and well known in Italy. Genovesi taught it in his letter to Antonio Conti in which, after examining whether ideas are the same as perceptions, he concludes: 'These reasons show clearly that ideas are the forms of our perceptions, the majority of which, that is, the first and simple forms, the basic elements of its knowledge, are received, not created by the mind. So let us go along with this view, which appears the most likely.' Ideas united to sensations by means of a judgment lead to the perception of bodies. These perceptions are composed of three elements: 1. pure ideas, simple apprehension of a thing (form), and 2. sensations (matter); 3. a judgment of the actual existence (bond between form and matter) which unites in a single object what is felt and the idea. However, all this will be discussed later.

(242) Critique of Pure Reason, Elementary Critique, Part 1 and Part 2, division 1, bk. 2, c. 2, section 3.

(243) Transcendental Logic, Analytic, bk.1, c. 1, section 3.

(244) Our communication with external reality is through sensation; Kant seems to have ignored this. Consequently, he was unable to reconcile the following two truths: 1. that we know what is real through concepts; 2. that sensible real things are different from our knowledge of them. Unable to reconcile them, he sacrificed the latter to the former.

(245) Reid is inclined to deny my view that this is posited by common sense; the impartial reader will judge. The difference of opinion, however, about the witness of common sense shows that its authority is not always sufficiently self-evident to convince all individuals, as some claim.