...necessary truths, such as we find in pure mathematics...must have principles whose proof does not depend on instances nor...on the testimony of the senses, even though without the senses it would never occur to us to think of them...[S]o the proof of them can only come from inner  principles described as innate. It would indeed be wrong to think that we can easily read these eternal laws of reason in the soul, as the Praetor's edict can be read on his notice-board, without effort or inquiry; but it is enough that they can be discovered within us by dint of attention...[W]hat  shows the existence of inner sources of necessary truths is also what distinguishes man from beast.

Beyond the world, i.e. beyond the collection of finite things, there is some one being who rules, not only as the soul is the ruler in me (or, to put it better, as the self is the ruler in my body), but also in a much higher way. For the one being who rules the universe doesn’t just govern the world but also builds or makes it. He is above the world and outside it, so to speak, and therefore he is the ultimate reason for things. ·That follows because he is the only extramundane thing, i.e. the only thing that exists out of the world; and nothing in the world could be the ultimate reason for things.

I now explain that second premise·. We can’t find in any individual thing, or even in the entire collection and series of things, a sufficient reason why they exist. Suppose that a book on the elements of geometry has always existed, each copy made from an earlier one, ·with no first copy·. We can explain any given copy of the book in terms of the previous book from which it was copied; but this will never lead us to a complete explanation, no matter how far back we go in the series of books. For we can always ask:

Why have there always been such books?

Why were these books written?

Why were they written in the way they were?

The different states of the world are like that series of books: each state is in a way copied from the preceding state—though here ·the ‘copying’ isn’t an exact transcription, but happens in accordance with certain laws of change. And so, ·with the world as with the books·, however far back we might go into earlier and earlier states we’ll never find in them a complete explanation for why there is any world at all, and why the world is as it is.

53. Now as there are an infinity of possible universes in the ideas of God, and but one of them can exist, there must be a sufficient reason for the choice of God which determines him to select one rather than another.

54. And this reason is to be found only in the fitness or in the degree of perfection which these worlds possess, each possible thing having the right to claim existence in proportion to the perfection which it involves.

55. This is the cause for the existence of the greatest good; namely, that the wisdom of God permits him to know it, his goodness causes him to choose it, and his power enables him to produce it.