Taken in the abstract, these rules are hardly very illuminating, and one can see some ground for Leibniz’s gibe that Descartes’s
rules of method were ‘like the precepts of some chemist; take what you need and do what you should, and you will get what you want’.1 But Descartes did not suppose that the Discourse explained his Method:
and he wrote to Vatier that neither the Discourse nor its accompanying treatises adequately expressed the Method (22 February 1638: I 559 ff., K. 45-6; the letter more generally sheds light on Descartes’s attitude to the book of 1637). But it is not just a matter of one work or a particular set of essays failing to explain fully the Method – no purely abstract treatment could. It is very much part of his outlook that actual exposure to intellectual problems is necessary to give any content to such maxims; the words gain meaning only from the experience of dealing with scientiﬁc questions themselves.