Descartes was prepared to go to any lengths in his search for certainty even to deny those things that seemed most self-evident. In his Meditations of 1641, and in the Objections and Replies that were included with the original publication, he set out to dismantle and then reconstruct the idea of the individual self and its existence. In doing so, Descartes developed a language of subjectivity that has lasted to this day and also took his first steps towards the view that would eventually be expressed in the epigram Cogito, ergo sum ('I think, therefore I am'), one of modern philosophy's most famous and most fiercely controversial claims.

The first part of a two-volume edition of Descartes' works in Penguin Classics, this edition includes extensive selections from the Objections and Replies, Part One of The Principles of Philosophy, Comments on a Certain Manifesto and related correspondence from 1643 to 1649.