Next Descartes turns to the possibility that the author of his existence is some being lesser than God, such as his parents. This, however, he rules out on the grounds that no being lesser than God could have created the idea of God that is in him. Since he has this idea, some being of infinite reality must have put it inside of him, and this being of infinite reality must thus be his creator. Descartes, in fact, argues that our idea of God, which is an innate idea, was placed in us by God as the artist's signature on his handiwork.
Before concluding that God is the author of his being, though, he considers one last possibility. Perhaps what caused this idea of infinite perfection in us is not a single being, but a whole collection of causes. In other words, perhaps we got the ideas of different perfections (e.g goodness, truth, eternality) from different sources. Descartes rules out this possibility on the grounds that unity, or the "inseparability of all the attributes of God," is one of the key components of our idea of God. Descartes is eager to point out that this extended argument for God as our creator, can double as yet a third argument for God's existence. If God must be posited in order to account for our existence, then God himself must exist.
One last issue that deserves attention from this section of the Principles is Descartes' discussion of the difference between the infinite and the indefinite. This conceptual analysis, which takes place at I.27, might sound like it is beside the point of the project at hand, but it is actually extremely important. It is intended as further proof that our idea of God can only be caused by God himself. As far as Descartes is concerned, there are only three possible ways that we could have arrived at the notion of the infinite. The first possibility is that we might have taken the idea of finitude and negated it in order to obtain the idea of the infinite. However, this would give us a negative idea of infinity, not a positive idea; we would think of infinity as a lack of finitude, when, really, it is the other way around. Alternatively, we might have started with our idea of the finite and extrapolated, continually adding more and more, until we recognized that we could potentially add on like this forever. This, Descartes, claims, is how we get to the idea of the indefinite. This method of extrapolation lands us with a vague sense that addition need never end, but it does not afford us with a positive conception of unendingness. Finally, there is the third possibility: God placed this idea in us. Given that there seems to be no other way that we could have arrived at this notion, Descartes concludes that this last scenario is the correct one.