Descartes writes that “the best way of achieving a firm knowledge of reality is first to accustom ourselves to doubting all things”; indeed, he recommends spending not merely “the short time needed” to read through the First Meditation program of doubt “but to devote several months, or at least weeks, to considering the topics dealt with” (AT VII 130, CSM II 94). When challenged by Hobbes – as to the originality of the skeptical arguments – Descartes replies that he “was not trying to sell them as novelties,” but instead had a “threefold aim”: first, to help distinguish what pertains “to the intellect … from corporeal things”; second, to “reply to them [these skeptical arguments] in the subsequent Meditations”; and, third, “to show the firmness of the truths … propound[ed] later on” (AT VII 171–72, CSM II 121).

There is unmistakable originality in Descartes’ pursuit of each of these aims, along with his introduction of (arguably) new skeptical hypotheses with more far-reaching consequences than anything before. The first aim and especially the third are closely associated with the methodological character of Cartesian doubt – the so-called method of doubt. Accordingly, doubts are pursued as a means, not an end: unlike the skeptics “who doubt only for the sake of doubting,” Descartes writes that his “aim was to reach certainty” (AT VI 28–29, CSM I 125). What follows is an overview of key elements of the method, emphasizing its use in the Meditations.

1. Knowledge and Doubt

The opening lines of the Meditations assert a connection between doubt and the foundations of knowledge: