History of Western Philosophy - Bertrand Russell [259]
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.
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; this is much the same as the second argument. Fourth, that we find various perfections in the world, and 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.
To return to the Summa contra Gentiles, having proved the existence of God, we can now say many things about Him, but these are all, in a sense, negative; God's nature is only known to us through what is not. God is eternal, since He is unmoved; He is unchanging, since He contains no passive potentiality. David of Dinant (a materialistic pantheist of the early thirteenth century) 'raved' that God is the same as primary matter; this is absurd, since primary matter is pure passivity, and God is pure activity. In God, there is no composition, therefore He is not a body, because bodies have parts.
God is His own essence, since otherwise He would not be simple, but would be compounded of essence and existence. (This point is important.) In God, essence and existence are identical. There are no accidents in God. He cannot be specified by any substantial difference; He is not in any genus; He cannot be defined. But He lacks not the excellence of any genus. Things are in some ways like God, in others not. It is more fitting to say that things are like God than that God is like things.
God is good, and is His own goodness; He is the good of every good. He is intelligent, and His act of intelligence is His essence. He understands by His essence, and understands Himself perfectly. (John the Scot, it will be remembered, thought otherwise.)
Although there is no composition in the divine intellect, God understands many things. This might seem a difficulty, but the things that He understands have no distinct being in Him. Nor do they exist per se, as Plato thought, because forms of natural things cannot exist or be understood apart from matter. Nevertheless, God must understand forms before creating. The solution of this difficulty is as follows: 'The concept of the divine intellect, according as He understands Himself, which concept is His Word, is the likeness not only of God Himself understood, but also of all the things of which