Rene Descartes 
Meditations on First Philosophy [EPUB ebook] 

Meditations on First Philosophy is a philosophical treatise written by Rene Descartes first published in Latin in 1641. The book is made up of six meditations, in which Descartes first discards all belief in things which are not absolutely certain, and then tries to establish what can be known for sure. The meditations were written as if he was meditating for 6 days: each meditation refers to the last one as yesterday. However, Descartes did not take 6 days to complete this work; it actually took several years.