This chapter concerns the early modern redefinition of psychology as the science of mind. It examines the way the “invention of mind” was incorporated into Descartes’s metaphysical project. This Cartesian innovation marked a rupture from the traditional science of the soul as a division of natural science or physics. Rejecting the Aristotelian partition of the soul into distinct powers and the Scholastic view of the principle of thought (the intellect) as only the highest psychic power, the new Cartesian psychology required the unity of the soul as the thinking substance. What constituted early modern psychology as a metaphysical science of mind, this chapter argues, was fundamentally Descartes’s “realist” thesis that mind is a thing (res). Together with this Cartesian substantialist view, its critical reception structured the modern science of mind. The early modern alternatives to Descartes’s ontological thesis about mind, the chapter highlights, were based either on the argument that mind is not a thing or on the argument that mind is a non-substantial thing, a mere mode. The chapter illustrates the first argument with Hobbes, the second with Regius and Spinoza.

This chapter focuses on the philosopher René Descartes. While Descartes is often seen as the initiator of modern habits of thinking – especially of the idea that the mind and body are distinct – here we view him as an outgrowth of Italian humanism. Descartes was educated by the Jesuits, at the time a new but influential religious order. From them, he imbibed Italian humanism’s respect for antiquity, its deep commitment to classical Latin, and most importantly its sometimes unarticulated through-line: that, to look at the world clearly, one needs to imagine oneself outside of it. But the Jesuits added something to Italian humanism: a deep respect for medieval Catholic theology, something that Descartes also took on board. His humanist education left him dissatisfied, however, laden with a feeling that it was not enough to establish a sure foundation on which could build a new way of looking at the natural world. Accordingly, he jettisoned the world of books, texts, and philology, grounding his perceptions of truth in the only thing about which he could be absolutely certain: that he existed. It is with Descartes that we can locate the beginnings of the modern separation of disciplines, as “natural philosophy” evolved into our modern natural sciences and separated itself from “philosophy” broadly conceived.