The views of Thomas on knowledge differ from those of many modern philosophers, in that he did not consider a critique of it indispensable at the beginning. Idealism had not been born, and not until Descartes do we find the method of doubt employed. Like other thinkers of his time, he accepted experience, the world, and a distinction between thought and that world. Fortunately we are able, however, to find scattered about his writings enough data to formulate a theory in answer to modern questions.
He admits that we should begin with doubt. "As that science (metaphysics) is concerned with the general consideration of truth, therefore to it also belongs general doubt about truth"*. But this doubt is not the same as that of Descartes. The latter professed to doubt about all, until he discovered one truth which would defy skepticism (cogito; ergo, sum). Thomas means only that we ought to test everything, even the first principles, to see if they are true. He does not hold that there is only one 'first indubitable truth'; there are many truths, and it is impossible to doubt them or suspend our judgment while searching for some more ultimate truth.
One amongst such truths is that we know reality. He belongs, therefore, to what is called the dogmatist tradition of philosophy, and he holds in one sense that the so-called problem of knowledge is a false problem. Knowledge cannot be justified by anything else save knowledge, and in its act it possesses its own justification. From this position he proceeds to realism, and this, once established, he builds thereon his whole metaphysic. His argument is in the Aristotelian mold. It is of the very nature of the intellect to know the real. The object (goal) of knowledge cannot be a creation of the mind nor just a subjective representation; to suppose the latter is to deny the objective validity of the sciences and, what is decisive, to deny the principle of contradiction.
If what I think at the present moment is wholly relative to me, then what my friend is thinking of may be the precise contradictory of it and yet equally true. Thus a certain form of realism is given as self-evident in the act of knowledge, and this can be shown by a reductio ad absurdum of any other standpoint. But it may be urged that what so far has been established is very little. A sceptic might deny the principles of contradiction and identity, and even granted their truth, they do not take us beyond the position of, for instance, Kant.
Validity in thought is consistent with almost any system of philosophy: idealist, subjectivist, as well as realist. St. Thomas has little difficulty in disposing of universal scepticism. He shows that we are forced to affirm; and whether we affirm knowledge or scepticism, or try to withhold judgment, we are making a statement about what is and what can be, and in that statement the first principles are necessarily applied. Nor, again, can these principles be laws of the mind and not of reality. Quite apart from the fact that, as someone has written, they 'declare not only an unthinkableness, but an impossibility', it can be shown that for the principle of contradiction to be true in the mind, it must also be true for reality. The reason is this: that if once I conceive of the possibility that there is a reality in which circles might be square, appearances not appearing, thinking not thinking, then even my own thought also may be possibly contradictory, and that is skepticism once more.
The principle of contradiction and knowledge of reality, therefore, go together. Usually Thomas does not bother with arguing this. No one, he says, 'can assent to the thought that he does not exist; for, in the very act of thinking, he perceives that he exists'. For him, the whole problem is concerned with this being which is revealed to thought, and though he has much to say on the nature of our knowledge, his views are as much dictated by metaphysical principles as by an analysis of the act of knowing.
In every affirmation, we affirm something; it is a declaration about the nature of reality, about what is or can be or cannot be; again, in every judgment the truth of the principle of identity or contradiction is also affirmed. In every judgment we can at least say, of any object before the mind, that it has being; it is not nothing and is identical with itself. Even what we commonly call nothing must be in some sense, and fall under the law of identity, and so be only relatively nothing. 'It is impossible that nothing could have ever existed'.
What we know first and always is being; in a vague, and confused way at first, and then more determinately, but never as anything other than being. To illustrate at the moment St. Thomas' theory of knowledge, however, it is worth pointing out how he speaks in an equivalent way of the certainty of truth, being, and first principles in pithy sayings, such as: 'The existence of truth, in general, is self-evident; that which the intellect conceives the first being, as it were, is very well known'.
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Originally Posted by Tankbuster
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