The first was never to accept anything as true that I did not plainly know to be such; that is to say, carefully to avoid hasty judgment and prejudic… - René Descartes

Divide each difficulty into as many parts as is feasible and necessary to resolve it.

The first was never to accept anything for true which I did not clearly know to be such; that is to say, carefully to avoid precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind so clearly and distinctly as to exclude all ground of doubt.

The second, to divide each of the difficulties under examination into as many parts as possible, and as might be necessary for its adequate solution.

Con frecuencia una falsa alegría vale más que una tristeza cuya causa es verdadera.

Finally, if there still are men who have not been sufficiently persuaded
of the existence of God and of their soul by means of the reasons I have
brought forward, I very much want them to know that all the other things
of which they think themselves perhaps more assured, such as having a
body, that there are stars and an earth, and the like, are less certain. For
although one might have a moral assurance about these things, which is
such that it seems one cannot doubt them without being extravagant, still
when it is a question of metaphysical certitude, it seems unreasonable for
anyone to deny that there is not a sufficient basis for one's being completely
assured about them, when one observes that while asleep one can, in the
same fashion, imagine that one has a different body and that one sees
different stars and a different earth, without any of these things being
the case. For how does one know that the thoughts that come to us in
dreams are any more false than the others, given that they are often no
less vivid and explicit? And even if the best minds study this as much as
they please, I do not believe they can give any reason sufficient to remove
this doubt, unless they presuppose the existence of God. For first of all,
even what I have already taken for a rule, namely that the things we very
clearly and very distinctly conceive are all true, is assured only for the
reason that God is or exists, and that he is a perfect being, and that all
that is in us comes from him.

La lectura de todos los buenos libros es como una conversación con los mejores ingenios de los pasados siglos que los han compuesto, y hasta una conversación estudiada en la que no nos descubren sino lo más selecto de sus pensamientos. [...] Es casi lo mismo conversar con gentes de otros siglos que viajar. Pero el que emplea demasiado tiempo en viajar acaba por tornarse extranjero en su propio país; y al que estudia con demasiada curiosidad lo que se hacía en los siglos pretéritos ocúrrele de ordinario que permanece ignorante de lo que se practica en el presente