Anselm - Proslogion (Selections)
Truly there is a God, although the fool has said in his heart, There is no God.
AND so, Lord, do you, who do give understanding to faith, give me, so far as you knowest it to be profitable, to understand that you are as we believe; and that you are that which we believe. And indeed, we believe that you are a being than which nothing greater can be conceived. Or is there no such nature, since the fool has said in his heart, there is no God? (Psalms xiv. 1). But, at any rate, this very fool, when he hears of this being of which I speak --a being than which nothing greater can be conceived --understands what be hears, and what he understands is in his understanding; although he does not understand it to exist.
For, it is one thing for an object to be in the understanding, and another to understand that the object exists. When a painter first conceives of what he will afterwards perform, he has it in his understanding, but be does not yet understand it to be, because he has not yet performed it. But after he has made the painting, be both has it in his understanding, and he understands that it exists, because he has made it.
Hence, even the fool is convinced that something exists in the understanding, at least, than which nothing greater can be conceived. For, when he hears of this, he understands it. And whatever is understood, exists in the understanding. And assuredly that, than which nothing greater can be conceived, cannot exist in the understanding alone. For, suppose it exists in the understanding alone: then it can be conceived to exist in reality; which is greater.
Therefore, if that, than which nothing greater can be conceived, exists in the understanding alone, the very being, than which nothing greater can be conceived, is one, than which a greater can be conceived. But obviously this is impossible. Hence, there is doubt that there exists a being, than which nothing greater can be conceived, and it exists both in the understanding and in reality.
God cannot be conceived not to exist. --God is that, than which nothing greater can be conceived. --That which can be conceived not to exist is not God.
AND it assuredly exists so truly, that it cannot be conceived not to exist. For, it is possible to conceive of a being which cannot be conceived not to exist; and this is greater than one which can be conceived not to exist. Hence, if that, than which nothing greater can be conceived, can be conceived not to exist, it is not that, than which nothing greater can be conceived. But this is an irreconcilable contradiction. There is, then, so truly a being than which nothing greater can be conceived to exist, that it cannot even be conceived not to exist;. and this being you are, O Lord, our God.
So truly, therefore, do you exist, O Lord, my God, that you can not be conceived not to exist; and rightly. For, if a mind could conceive of a being better than you, the creature would rise above the Creator; and this is most absurd. And, indeed, whatever else there is, except you alone, can be conceived not to exist. To you alone, therefore, it belongs to exist more truly than all other beings, and hence in a higher degree than all others. For, whatever else exists does not exist so truly, and hence in a less degree it belongs to it to exist. Why, then, has the fool said in his heart, there is no God (Psalms xiv. 1), since it is so evident, to a rational mind, that you do exist in the highest degree of all? Why, except that he is dull and a fool?
How the fool has said in his heart what cannot be conceived. --A thing may be conceived in two ways: (1) when the word signifying it is conceived; (2) when the thing itself is understood As far as the word goes, God can be conceived not to exist; in reality he cannot.
BUT how has the fool said in his heart what he could not conceive; or how is it that he could not conceive what he said in his heart? since it is the same to say in the heart, and to conceive.
But, if really, nay, since really, he both conceived, because he said in his heart; and did not say in his heart, because he could not conceive; there is more than one way in which a thing is said in the heart or conceived. For, in one sense, an object is conceived, when the word signifying it is conceived; and in another, when the very entity, which the object is, is understood.
In the former sense, then, God can be conceived not to exist; but in the latter, not at all. For no one who understands what fire and water are can conceive fire to be water, in accordance with the nature of the facts themselves, although this is possible according to the words. So, then, no one who understands what God is can conceive that God does not exist; although he says these words in his heart, either without any or with some foreign, signification. For, God is that than which a greater cannot be conceived. And he who thoroughly understands this, assuredly understands that this being so truly exists, that not even in concept can it be non-existent. Therefore, he who understands that God so exists, cannot conceive that he does not exist.
I thank you, gracious Lord, I thank you; because what I formerly believed by your bounty, I now so understand by your illumination, that if I were unwilling to believe that you do exist, I should not be able not to understand this to be true.
God is whatever it is better to be than not to be; and he, as the only self-existent being, creates all things from nothing.
WHAT are you, then, Lord God, than whom nothing greater can be conceived? But what are you, except that which, as the highest of all beings, alone exists through itself, and creates all other things from nothing? For, whatever is not this is less than a thing which can be conceived of. But this cannot be conceived of you. What good, therefore, does the supreme Good lack, through which every good is? Therefore, you are just, truthful, blessed, and whatever it is better to be than not to be. For it is better to be just than not just; better to be blessed than not blessed.
Source: The Internet Medieval Sourcebook.