Descartes' Meditations on First Philosophy is, indisputably, one of the greatest philosophical classics of all time. The challenge it offers is in many ways definitive of the philosophical enterprise: to leave behind the comfortable world of inherited prejudice and preconceived opinion; to take nothing for granted in the determination to achieve secure and reliable knowledge. Descartes talks of ‘demolish[ing] everything completely and start[ing] again right from the foundations', and for this purpose he famously uses doubt, stretched to its limits, as an instrument which self-destructs, impelling him forwards on the journey towards certainty and truth. These central themes are today part of every introductory course in the philosophy of knowledge: Descartes' masterpiece has achieved canonical status in that part of the philosophy syllabus we now call ‘epistemology’. Yet for Descartes himself these epistemic concerns were but one part of a much wider project, the construction of a grand, all-embracing system of philosophy which would encompass metaphysics, natural science, psychology and morals, connecting all the objects within the scope of human understanding. In the words of the famous metaphor which he deployed some six years after the publication of the Meditations, ‘the whole of philosophy is like a tree. The roots are metaphysics, the trunk is physics, and the branches … all the other sciences.

Descartes spent much of his career occupied with what we would nowadays call theoretical physics: he devised a radical new theory of the nature of matter, defined simply as extension in three dimensions, and formulated a number of mathematical laws describing the results of collisions of moving particles of matter. He then proposed to apply these principles to a wide variety of subjects, from cosmology and astronomy to physiology and medicine; and towards the end of his life he planned to include a science of man, which would develop prescriptions for how to understand and control the workings of our bodies, and how to live fulfilled and worthwhile lives.