Appendix 2.
(442) [St. Thomas on knowledge]
All this teaching may be found in the corpus of knowledge handed down to us by our predecessors. St. Thomas (Contra Gent., III, q. 46) teaches that our soul needs an intelligible species in order to know itself, just as it does to know other things. 'Intelligible species', as I shall show later, is to be understood simply as a universal idea to which the soul (this particular ens) adheres as to its genus, or rather its major predicate. The soul, therefore, is known through the light of the acting intellect (the idea of being) in the same way as other beings. Here, too, St. Thomas distinguishes between the matter and form of knowledge. With its feeling of self, the soul provides only the matter of knowledge. This matter, informed through an innate light, becomes true knowledge. St. Thomas says:
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Natural knowledge is that which comes about through something placed in us by nature (naturaliter nobis additum). Of this kind are the indemonstrable principles known through the light of the acting intellect. If we knew the soul by means of the soul itself, this too would be natural knowledge. But in things known to us by nature, there is no error... Man does not err in his knowledge of principles. There would be no error, therefore, about the substance of the soul if this were known to us per se. But it is obviously false that the soul is known per se. |
He goes on a little later:
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What is known per se must be known prior to everything known mediately. Per se knowledge, like first propositions related to conclusions, is the principle of knowledge related to mediate knowledge. But if the soul were to know its own substance through itself, it would be known per se, and consequently would be the first thing known and the principle of knowledge of everything else. But this is obviously false. The substance of the soul is not admitted and presumed as something already known. It has to be investigated and deduced from the principles. |
These quotations show that: 1. St. Thomas admitted knowledge of the principles prior to particular knowledge of the soul; 2. knowledge of our own soul is impossible without knowledge of the principles; 3. the first principles are known per se and immediately through the innate light which, as we have shown elsewhere and go on repeating, can only be the idea of being; 4. the soul, known through the same principles governing our knowledge of other things, is neither what is first known nor the principle of knowledge of other things. It cannot, therefore, be the source whence we deduce universal ideas and principles, as Descartes and many others thought. Rather, knowledge of the soul has to be deduced from the universal principles.
Aristotle recognised this truth when he said that the possible intellect knows itself in the same way as it knows other things (De Anima, bk. 3, 45).