For I found myself embarrassed with so many doubts and errors that it seemed to me that the effort to instruct myself had no effect other than th eincreasing discovery of my own ignorance

If I found any new truths in the sciences, I can say that they follow from, or depend on, five or six principal problems which I succeeded in solving and which I regard as so many battles where the fortunes of war were on my side.

Reason is nothing without imagination.

How do we know that anything really exists, that anything is really the way it seems ot us through our senses?

There is nothing so far removed from us as to be beyond our reach, or so hidden that we cannot discover it.

Neither the true nor the false roots are always real; sometimes they are imaginary; that is, while we can always imagine as many roots for each equation as I have assigned, yet there is not always a definite quantity corresponding to each root we have imagined.

...it is certain that I am really distinct from my body, and can exist without it.