The Three Self-Evident Truths

In our consideration of Argument - indeed, in our consideration of Reason - we must accept what are called the Three Self-Evident Truths. These are not debatable, and are not provable. Like the axioms of Geometry, they are "Given" - they are starting points without which one cannot proceed. We need to know them - and know them well.

1. The First Fact is "the existence of the thinking subject". I (who am presently thinking about something) exist.

2. The First Principle is "the principle of contradiction": A thing cannot both BE and NOT BE in the same way at the same time.

3. The First Condition of Certain Knowledge is "the natural capacity of our reason to know the truth". Our brains, minds, reasoning powers are ABLE to know the truth of things. Truth in the general sense is NOT a "mystery" which cannot be attained.

Perhaps the tightest statement which summarizes all this as a basis for thought is this famous little fragment from one of Chesterton's letters:

A cosmos one day being rebuked by a pessimist replied, "How can you who revile me consent to speak by my machinery? Permit me to reduce you to nothingness and then we will discuss the matter."
Moral. You should not look a gift universe in the mouth.
[quoted in Ward's Gilbert Keith Chesterton 49-50]

This is often taken to mean a variety of things, but it clearly means that one CANNOT begin "questioning" the reality we live in - that is the Universe - if one is going to DENY it, or his own existence, or his ability to obtain answers, or his ability to grasp the answers when they appear. Hence, it is the perfect Scholastic answer, and can be used against all manner of Dark philosophers.

Here is more of Shallo's presentation of them:

93. These three self-evident truths are implied and necessarily admitted in every judgment, viz.: the existence of the thinking subject, the principle of contradiction, the natural capacity of our reason to know the truth, i. e., the first fact, the first principle, the first condition of certain knowledge.

Proof. If any of them be denied or doubted, there can be no certitude. For there can be no thought without an existing thinker. There can be no certitude if two contradictories can be simultaneously true. There can be no certitude, if the mind is incapable of certitude.

These three truths cannot be demonstrated without begging the question; for they are, and must be, assumed in every demonstration, since there can be no certain premise in which they are not implied and necessarily admitted.

Note 1. Nor need they be demonstrated, for they are self?evident, and in their very denial are affirmed.

Note 2. Hence the absurdity of Kant's criticism or examination of the reliability of reason in its perception of truth. In his examination he employs the very faculty of whose reliability he professes to doubt, and hence involves himself in the contradiction essential to all scepticism.

Note 3. Hence, too, the absurdity of Descartes' "Methodical Doubt," as he calls it. He held that a philosopher should try to doubt about all things, until they are demonstrated. Finding he could not doubt of the existence of his own thought, he takes this as the one principle of all philosophy, and thence argues, "I think, therefore I am." But this argument is good for nothing, unless the principle of contradiction and the infallibility of the reason, which perceives and affirms the fact of its own existence, be admitted as true. And even granting the premise, how is the conclusion certain if reason which deduces it be unreliable? Further, if all our other natural faculties are unreliable, why should not the faculty of consciousness, which tells me I think, be so too?
[Shallo, Scholastic Philosophy 101-2]

Wonderful. Now you know.

Here is one of the most splendid of GKC's commentaries on them:

...even those who appreciate the metaphysical depth of Thomism in other matters have expressed surprise that he [St. Thomas Aquinas] does not deal at all with what many now think the main metaphysical question; whether we can prove that the primary act of recognition of any reality is real. The answer is that St. Thomas recognised instantly, what so many modern sceptics have begun to suspect rather laboriously; that a man must either answer that question in the affirmative, or else never answer any question, never ask any question, never even exist intellectually, to answer or to ask. I suppose it is true in a sense that a man can be a fundamental sceptic, but he cannot be anything else; certainly not even a defender of fundamental scepticism. If a man feels that all the movements of his own mind are meaningless, then his mind is meaningless, and he is meaningless; and it does not mean anything to attempt to discover his meaning. Most fundamental sceptics appear to survive, because they are not consistently sceptical and not at all fundamental. They will first deny everything and then admit something, if for the sake of argument - or often rather of attack without argument. I saw an almost startling example of this essential frivolity in the professor of final scepticism, in a paper the other day. A man wrote to say that he accepted nothing but Solipsism, and added that he had often wondered it was not a more common philosophy. Now Solipsism simply means that a man believes in his own existence, but not in anybody or anything else. And it never struck this simple sophist, that if his philosophy was true, there obviously were no other philosophers to profess it.

To this question "Is there anything?" St. Thomas begins by answering "Yes"; if he began by answering "No", it would not be the beginning, but the end. That is what some of us call common sense. Either there is no philosophy, no philosophers, no thinkers, no thought, no anything; or else there is a real bridge between the mind and reality.
[GKC St. Thomas Aquinas CW3:515-6]

Ah, again we see this idea of Engineering - the idea that the Scholastic way is productive and efficient - it gets things DONE. It builds a bridge. It is not for nothing that the Pope is called by the ancient Roman title of Pontifex Maximus - the Supreme Pontiff, the Greatest Bridge-Builder.

Repeat this, please:

To this question "Is there anything?" St. Thomas begins by answering "Yes"; if he began by answering "No", it would not be the beginning, but the end. That is what some of us call common sense.

Yes: it is indeed Common Sense. It is sound, excellent, engineering. If we want a bridge, we need good foundations. These three truths are the most solid foundations existing, and if we expect to do anything at all, we must start there.