Summary: Rules for the Direction of the Mind

In this work, Descartes lays out various rules for a universal method to guide thought in its pursuit of truth.

Rule 1: we must seek to enunciate sound and true judgements about everything that presents itself to [the mind] ¹.

This first rule gives Descartes occasion to develop an important idea: we should not adopt, in science, the principle of specialisation — that is, the restriction to a single science.

Specialisation is necessary in the arts: one becomes a master — a virtuoso of the violin, for instance — only by dedicating oneself entirely to one's art: It is not the hands of the same man that can become accustomed to cultivating the fields and playing the zither ².

To reach truth, however, we must avoid restricting ourselves to a single science. Here Descartes develops a critique of the fragmentation of the sciences — prevalent in his time as in ours — arguing that they should be reabsorbed into a unified science.

The unity of the sciences arises from their essential common ground:

All the sciences are nothing other than human wisdom, which always remains one and identical with itself, however different the objects to which it applies may be, and which receives no more diversity from them than the light of the sun receives from the variety of things it illuminates.³.

This unity is therefore what Descartes calls universal wisdom ⁴ — or good sense.

Man has chosen to confine himself to discovering truths through specialisation in particular disciplines — whereas each truth discovered in fact helps us uncover others, even in quite different fields.

The aim of study should be this general end (universal wisdom), rather than any particular end. Utility or happiness are examples of particular ends that some sciences wrongly pursue. The sciences should not be pursued solely to improve human existence.

This would, if we sought only that, cause us to omit many things necessary to arrive at other knowledge, because they appear at first sight to be devoid of interest or utility ⁵. We would not, for instance, study what occurs in some distant galaxy — too remote ever to be reached — as it would seem of no practical use to humanity.

What, then, should we do? On the contrary, we must persuade ourselves that all the sciences are so closely linked together that it is much easier to learn them all together than to separate one from all the others ⁶.

We should also strive to develop the natural light of [our] reason ⁷. This will allow us to progress far more swiftly than those who confine themselves to particular sciences.

Rule 2: We should deal only with those objects of which our mind seems able to attain a certain and indubitable knowledge ⁸.

The doubtful, the probable, and the uncertain must be avoided. This principle, which also appears in the Meditations on First Philosophy, is central to Descartes's thought. If we introduce doubt into our reasoning by accepting merely probable arguments, then the hope of extending our knowledge is not so great as the risk of diminishing it ⁹.

On the contrary, we must seek what is certain, evident, and necessary — and by ascending from one certain proposition to another, we may arrive at indubitable truths.

Yet, it might seem that such truths are very rare. Descartes replies that they are far more numerous than we think, and suffice to demonstrate rigorously innumerable propositions, on which they have hitherto been able to state nothing better than probabilities ¹⁰.

And yet, it seems that no idea commands consensus within the scientific community, nor can any be presented as an indubitable universal truth.

Descartes argues, however, that there is one field in which such universal assent exists — at least in his time: arithmetic and geometry. These disciplines were to serve as a model: the mind should strive to attain human wisdom by adopting the same methods and the same standards of certainty as those of mathematics.

¹ Les Règles pour la direction de l’esprit, le Livre de poche, Paris, 2002 p.75
² Ibid.
³ p.76
⁴ Ibid.
⁵ p.77
⁶ Ibid.
⁷ Ibid.
⁸ p.78
⁹ Ibid.
¹⁰ Ibid.