The incomplete and posthumously published Regulae ad directionem ingenii is one of Descartes’ earliest major writings and was included in the posthumous inventory of his effects (under item F). It was first published in a Dutch translation in 1684 (version N). In 1670 Leibniz obtained a copy of the Latin manuscript in Paris (version H). The Latin text was first published in Opuscula posthuma (1701, the “standard” version, known as A). Some passages also appeared in French translation in the Port-Royal Logic of Arnauld and Nicole (1662) and in Baillet's Vie de Descartes (1691). A previously unknown copy of an apparently earlier version was discovered in Cambridge University Library in 2011 (version C).

The title is appropriate but likely the invention of editors. In English it is typically called Rules for the Direction of the Mind, but better alternatives for ingenium have been proposed, like “spirit,” “native intelligence,” or “total mind-body equipment.” The work is about the proper method of knowing and the guidance of the mind in thinking and discovery. It was planned to be in three parts, each consisting of twelve rule-rubrics plus elaboration, but only the first twenty-one rubrics exist (the last three without elaboration).

The first part treats problem solving (quaestiones) in general. Rule 3 attributes all knowing to two human powers (intuition and deduction, the latter derivative of the former, without a sharp boundary dividing the two). They must be used methodically and employ a fundamental kind of mathematics, called mathesis universalis in the second half of Rule 4, to break down what is complicated into what is simple (Rule 5). Order and measure must be established among all things apprehended by the mind by “proportionalizing” the degree to which the things being considered contain or participate in natures and, ultimately, in simple natures (Rule 6; the simple natures are further discussed in Rules 8 and 12). Rule 7 emphasizes that the completion of knowledge requires that “every single thing … must be surveyed in a continuous and wholly uninterrupted sweep of thought” (or imagination). It also introduces the operation of enumeration (also called induction) to assure that solutions are complete and distinct, especially when we “infer a proposition from many disconnected propositions.” It may be performed either completely or merely sufficiently – for example, the latter when we can readily assign the matters in question to conveniently chosen classes.