What I have given in the second book on the nature and properties of curved lines, and the method of examining them, is, it seems to me, as far beyon… - René Descartes

Zira öyle çok kuşku ve yanılgıyla kuşatılmış bulunuyordum ki kendimi yetiştiremeye çalışırken elde ettiğim tek kazanç gitgide cahilliğimi görmeye başlamış olmam gibi geliyordu bana.

M. Desargues puts me under obligations on account of the pains that it has pleased him to have in me, in that he shows that he is sorry that I do not wish to study more in geometry, but I have resolved to quit only abstract geometry, that is to say, the consideration of questions which serve only to exercise the mind, and this, in order to study another kind of geometry, which has for its object the explanation of the phenomena of nature... You know that all my physics is nothing else than geometry.

In order to determine whether we can know anything with certainty, we first have to doubt everything we know