All that I have, up to this moment, accepted as possessed of the highest truth and certainty, I received either from or through the senses. I observe… - René Descartes

It is only prudent never to place complete confidence in that by which we have even once been deceived.

Pues tales frutos he recogido ya de ese método, que, aun cuando, en el juicio que sobre mí mismo hago, procuro siempre inclinarme del lado de la desconfianza mejor que del de la presunción, y aunque, al mirar con ánimo filosófico las distintas acciones y empresas de los hombres, no hallo casi ninguna que no me parezca vana e inútil

Viver sem filosofia é exatamente como ter os olhos fechados sem nunca procurar abri-los.

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.