Summary: Rules for the Direction of the Mind

In this work, Descartes sets 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 offers Descartes an opportunity to develop an important idea: we should not adopt, in science, the principle of specialisation, namely the study of a single science.

Specialisation is necessary in the arts: one becomes a master (for example, a virtuoso of the violin) only by dedicating oneself solely to the object of 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—current in his time, as in ours—which, he argues, 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.

Unity is therefore this universal wisdom ⁴, which Descartes also calls good sense.

Man has chosen to limit himself to discovering truths through specialisation in particular disciplines, whereas, on the contrary, each truth discovered aids us in uncovering others, even in 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 at which some sciences wrongly aim. The sciences should not be pursued solely for the purpose of improving 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. For example, we would not study what occurs in some distant galaxy, so far away that we could never reach it, as it would seem of no practical use to humanity.

So, what 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 enable us to progress much faster 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 fundamental to Descartes' 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 discover 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.

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

However, Descartes argues that there is one field in which such universal assent exists (at least in his time): it is 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 demand for certainty as those found in 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.