[Descartes] And so it was he who discovered the gulf between the subjective or ideal and the objective or real. He clothed this insight in the form of a doubt concerning the existence of the external world; but by his inadequate solution of such doubt, namely that God Almighty would surely not deceive us, he has shown how profound the problem is and how difficult it is to solve.
parerga And Paralipomena: Short Philosophical Essays, Vol 1: Parergaby arthur Schopenhauer
The latter had assumed the reality of the external world on the credit of God; and here, of course, it seems strange that, whereas the other theistic philosophers endeavour to demonstrate the existence of God from that of the world, Descartes, on the contrary, proves the existence of the world first from the existence and trustworthiness of God; it is the cosmological proof the other way round. Here too Malebranche goes a step farther and teaches that we see all things immediately in God himself. This certainly is equivalent to explaining something unknown by something even more unknown.
