  As the authors of the Logic make clear, this particular part of their text derives from Descartes's Rules for the  Direction of the Mind, written around 1627, but only published  posthumously in 1684. The specification of the four types was most  likely offered in elaborating Descartes's Rule Thirteen, which  states: “If we perfectly understand a problem we must abstract  it from every superfluous conception, reduce it to its simplest terms and, by means of an enumeration, divide it up into the smallest  possible parts.” (PW, I, 51. Cf. the editorial  comments in PW, I, 54, 77.) The decompositional conception  of analysis is explicit here, and if we follow this up into the later Discourse on Method, published in 1637, the focus has  clearly shifted from the regressive to the decompositional conception of analysis. All the rules offered in the earlier work have now been  reduced to just four. This is how Descartes reports the rules he says he adopted in his scientific and philosophical work: