PART ONE

THE CRITERION OF CERTAINTY

CHAPTER 6

The principle of knowledge must also be
the principle of certainty

1059. When I want to know whether a proposition is true or false, I seek its reason (cf. 1055–1058).
This reason can be expressed by another proposition, whose reason I also want to know. In order to be completely satisfied,(15) I move from one proposition to another, from one reason to another, until I reach the self-evident ultimate reason. I then say I have grasped the truth of the first proposition intuitively, because I have the supreme principle of its certainty.

We must pay careful attention to this fact.(16) As long as we are investigating the truth or falsity of a proposition, we distinguish between knowledge and certainty. We may know and understand the sense of the proposition without knowing whether it is true; our knowledge of the proposition is not the same as the truth or certainty we are looking for. This distinction between the knowledge and certainty of a proposition is present in the whole series of propositions or reasons, until we reach the final reason. When we have reached the ultimate reason, knowledge necessarily becomes one with certainty without any real separation remaining between them.

In fact, I called ultimate reason any proposition which, when understood, draws our assent by its own intrinsic authority and power. If we are speaking seriously and do not wish to complicate what is clear, we can neither desire nor look for another reason because the reason we now have is seen as justified in itself, and satisfies us fully. As soon as we know the ultimate reason, we say we see the truth of the matter (cf. 1055–1058). Knowledge and certainty identify in such a way, therefore, that at the point where our investigation ends, knowledge is also certainty for us.

1060. Note, however, that we do not stop at the ultimate reason simply because we feel satisfied with it. We could be satisfied even with a non-ultimate reason, and go no further. We stop at the ultimate reason necessarily as well as willingly. ‘Ultimate’ means the reason beyond which we cannot truly find any other reason or give any assent or know anything further except by deceiving ourselves. The ultimate reason of a proposition, therefore, is the terminal point of our knowledge as well as of our assent and persuasion. It is the principle both of certainty and of knowledge, as I proposed to show.(17)

(15) In fact, human beings are not always reasonably satisfied with their investigations. Sometimes they are satisfied by frivolous reasons, as people en masse often are. These reasons are often more striking than solid, true reasons. We can therefore ask what is the law according to which human beings find satisfaction in their search for the reasons of things, and we can determine it as: ‘In a series of subordinate propositions, human beings find satisfaction when they have reached a proposition they no longer doubt,’ whatever the cause removing the doubt.

(16) Note that I have not yet answered the sceptics. I am simply presenting the facts, and analysing them. I am describing what happens to human beings, and what they think happens to them. In other words, I am talking about people in general, not sceptics, whose position I will discuss later.

(17) When this point has been reached where knowledge, truth and certainty are one single thing, we see how absurd it is to try to produce knowledge from the senses, which cannot generate certainty. The Peripatetics saw that judgment about the truth of things could not be a property of the senses. This should have been sufficient (if people had carefully reflected on the matter) for them to be aware that knowledge could not derive from the senses as from its formal cause, because ultimately knowledge is the same as certainty. Cicero, referring to the opinion of the Peripatetics and Academicians, says, Tertia philosophiae pars, quae erat in ratione et disserendo, sic tractabatur ab utrisque (the Academicians and the Peripatetics). Quamquam oriretur a sensibus, tamen non esse iUDICIUM VERITATIS in sensibus. Mentem volebant rerum esse iudicem: solam censebant idoneam cui crederetur, quia sola cerneret id quod semper esset simplex, et unius modi, et tale quale esset. Hanc illi IDEAM appellabant, iam a Platone ita appellatam: nos recte speciem possumus dicere [Both (the Academicians and the Peripatetics) dealt with the third part of philosophy, which consisted of reasoning and discussion. The JUDGMENT OF TRUTH, although aroused by the senses, is not in the senses. These philosophers considered the mind as judge of things. Only the mind can be believed, because the mind alone discerns what is always simple and of one kind, and discerns it exactly as it is. This they called ‘IDEA’, as Plato had, although we can rightly call it ‘species’] (Acad., 1). Thus, the Peripatetics made ideas the principle of certainty. But if they had noticed how one idea is generated from another, they would have found the first idea, source of all other ideas, and hence the unity of the source of knowledge and certainty. Whatever the Peripatetics thought, it is certain that anyone realising that the judgment of certainty comes only from the mind, can discover (if he intends to be coherent with himself) that knowledge also must have the same origin.