This new Penguin edition includes the Meditations and selections from Principles of Philosophy and avoids repetition by omitting the simpler Discourse on Method. The Meditations is a keystone of 'modern' (as opposed to Medieval) philosophy and takes as its starting point the reconstruction of knowledge on a basis of absolute certainty. Hence Descartes begins by enumerating his inherited beliefs and subjecting them to the famous 'Cartesian doubt' ('Cartesian' from 'des Cartes'). This reduces him to the famous 'I think, I am' as indubitable. From there, he builds up a system of knowledge on the basis of arguments, starting with the existence of God and modeled on mathematical argumentation.
Used as a teaching text, Descartes can reduce students to a frustrated scepticism, as can Hume's
Treatise of Human Nature. One wise professor who used Descartes as a class text taught it alongside
Francis Bacon's writings which summarise the wealth and detail of knowledge, classified into history, poetry and philosophy to counteract abstract scepticism. Descartes was also contrasted in the 19th century with
Blaise Pascal's Pensées, which says that 'the heart has its reasons that reason does not know' and thus rounded out the rationalistic idea of experience. Amongst modern critics, John Macmurray's
The Self as Agent argues that it is incoherent to separate knowledge and practice.