La recherche de la vérité par la lumière naturelle is the title given to a dialogue among three people, Poliander, Epistemon, and Eudoxe, in which Poliander represents the views of a gentleman of good breeding but without any formal education in philosophy; Epistemon, the position of a traditional philosopher who has read extensively in philosophical literature; and Eudoxe, the position of a Cartesian, who relies on his own intelligence. The intention is to show that, as long as one uses one's common sense, it is not difficult to choose between the traditional approach to philosophy, which relies on reading, memory, and authority, and the Cartesian approach, which relies on one's own intelligence. The dialogue form, which is unique in Descartes’ work, could be an experiment in style or an imitation of Galileo. However, the underlying technique of confronting the two approaches and leaving it to the common reader to decide is, to a certain extent, familiar from Descartes’ other works, like the planned but never realized sequel to the Discourse on Method (1637), the Objections and Replies that accompany the Meditations (1641), and even the Principles of Philosophy (1644).

Unfortunately, the Search for Truth was left unfinished. And although it was clearly meant as a complete exposition of Descartes’ philosophy (AT X 505–6), the text hardly reaches beyond the first stage – namely, the decision to call everything into doubt and the cogito. In that sense, the work does not add much to the Discourse and the Meditations. However, that makes it even more frustrating that we do not know when Descartes wrote it. Some place it at the beginning of Descartes’ career, even before 1631 (Carraud and Olivo 2013); others, somewhere in the middle, suggesting that it may have been written for Constantijn Huygens (see Alquié 1973, II, 1101–4), whereas others place it at the end of his career, in the belief that it was written for Queen Christina (Cassirer 1942). This much is clear: like the Discourse on Method (1637) and the Passions of the Soul (1649) the dialogue was written for a nonacademic audience, whereas the Meditations and the Principles are meant for specialists.