Anselm of Canterbury on Divine Command Theory
Cur Deus Homo ("Why God Became Man") (1033-1109).
When it is said that what God wishes is just, and that what He does not wish is unjust, we must not understand that if God wished anything improper it would be just, simply because he wished it. For if God wishes to lie, we must not conclude that it is right to lie, but rather that he is not God. For no will can ever wish to lie, unless truth in it is impaired, nay, unless the will itself be impaired by forsaking truth. When, then, it is said: "If God wishes to lie," the meaning is simply this: "If the nature of God is such as that he wishes to lie;" and, therefore, it does not follow that falsehood is right, except it be understood in the same manner as when we speak of two impossible things: "If this be true, then that follows; because neither this nor that is true;" as if a man should say: "Supposing water to be dry, and fire to be moist;" for neither is the case. Therefore, with regard to these things, to speak the whole truth: If God desires a thing, it is right that he should desire that which involves no unfitness. For if God chooses that it should rain, it is right that it should rain; and if he desires that any man should die, then is it right that he should die. Wherefore, if it be not fitting for God to do anything unjustly, or out of course, it does not belong to his liberty or compassion or will to let the sinner go unpunished who makes no return to God of what the sinner has