Chapter XIII: ST Thomas Aquinas
St Thomas’s most important work was the Summa contra Gentiles (1259–64). It tried to establish the truth of Christianity by arguments to a non-Christian, likely a man versed in the philosophy of the Arabs. His other book, Summa Theologiae, is of equal importance, but it assumes the truth of Christianity before presenting its arguments.
What follows is an abstract of the Summa contra Gentiles
The first step is to prove the existence of God. Some think this unnecessary, since the existence of God (they say) is self-evident. If we knew God’s essence, this would be true, since (as is proved later) in God, essence and existence are one. But we do not know His essence, except very imperfectly. Wise men know more of His essence than do the ignorant, and angels know more than either; but no creature knows enough of it to be able to deduce God’s existence from His essence. On this ground, the ontological argument is rejected.It is important to remember that religious truths which can be proved can also be known by
faith. The proofs are difficult, and can only be understood by the learned; but faith is necessary also to the ignorant, to the young, and to those who, from practical preoccupations, have not the leisure to learn philosophy. For them, revelation suffices.Some say that God is only knowable by faith. They argue that, if the principles of demonstration became known to us through experience derived from the senses, as is said in the Posterior Analytics, whatever transcends sense cannot be proved. This, however, is false; and even if it were true, God could be known from His sensible effects.
The existence of God is proved, as in Aristotle, by the argument of the unmoved mover.2 There are things which are only moved, and other things which both move and are moved. Whatever is moved is moved by something, and, since an endless regress is impossible, we must arrive somewhere at something which moves other things without being moved. This unmoved mover is God. It might be objected that this argument involves the eternity of movement, which Catholics reject. This would be an error: it is valid on the hypothesis of the eternity of movement, but is only strengthened by the opposite hypothesis, which involves a beginning, and therefore a First Cause.
Bertrand Russell, A History of Western Philosophy
In the Summa Theologiae, five proofs of God’s existence are given. First, the argument of the unmoved mover, as above. Second, the argument of the First Cause, which again depends upon the impossibility of an infinite regress. Third, that there must be an ultimate source of all necessity; similar to the second argument. Fourth, that we find various perfections in the world – that these must have their source in something completely perfect. Fifth, that we find even lifeless things serving a purpose, which must be that of some being outside them, since only living things can have an internal purpose.
Now to the question that troubled both Plato and Aristotle. Can God know particular things, or does He only know universals and general truths? A Christian, since he believes in Providence, must hold that God knows particular things, but there are strong arguments against this view.
St Thomas lists seven such arguments, and then refutes them. The seven arguments are as follows:
Bertrand Russell, A History of Western Philosophy
1. Singularity being signate matter, nothing immaterial can know it.
2. Singulars do not always exist, and cannot be known when they do not exist; therefore they
cannot be known by an unchanging being3. Singulars are contingent, not necessary; therefore there can be no certain knowledge of
them except when they exist.
4. Some singulars are due to volitions, which can only be known to the person willing.
5. Singulars are infinite in number, and the infinite as such is unknown.
6. Singulars are too petty for God’s attention.
7. In some singulars there is evil, but God cannot know evil.
Aquinas replies that God knows singulars as their cause; that He knows things that do not yet exist, just as an artificer does when he is making something; that He knows future contingents, because He sees each thing in time as if present, He Himself being not in time; that He knows our minds and secret wills, and that He knows an infinity of things, although we cannot do so. He knows trivial things, because nothing is wholly trivial, and everything has some nobility; otherwise God would know only Himself.
And the order of the universe is noble, and that cannot be known without knowing even the trivial parts. Finally, God knows evil things, because knowing anything good involves knowing the opposite evil.
While Aquinas does engage in philosophy, there is lacking a true philosophic spirit in Aquinas, in the opinion of Russell.
Unlike the Platonic Socrates, he does not set out to follow wherever the argument may lead. Aquinas is not engaged in an enquiry, the result of which it is impossible to know in advance. Before he begins to philosophize, he already knows the truth; it is declared in the Catholic faith. If he can find apparently rational arguments for some parts of the faith, so much the better; if he cannot, he need only fall back on revelation. The finding of arguments for a conclusion given in advance is not philosophy, but special pleading. I cannot, therefore, feel that he deserves to be put on a level with the best philosophers either of Greece or of modern times.
Bertrand Russell, A History of Western Philosophy