Lisa Downing

The prominent place of corpuscularian mechanism in Locke's Essay is nowadays universally acknowledged. Certainly, Locke's discussions of the primary/secondary quality distinction and of real essences cannot be understood without reference to the corpuscularian science of his day, which held that all macroscopic bodily phenomena should be explained in terms of the motions and impacts of submicroscopic particles, or corpuscles, each of which can be fully characterized in terms of a strictly limited range of properties: size, shape, motion, and, perhaps, solidity or impenetrability. Indeed, Locke's lists of primary qualities are quite consistent with those found in the work of his friend Robert Boyle, a prominent defender of the corpuscularian program; his real essences of substances appear to be corpuscular constitutions, arrangements of particles.

Although George Berkeley himself made no major scientific discoveries, nor formulated any novel theories, he was nonetheless actively concerned with the rapidly evolving science of the early eighteenth century. Berkeley's works display his keen interest in natural philosophy and mathematics from his earliest writings (Arithmetica, 1707) to his latest (Siris, 1744). Moreover, much of his philosophy is fundamentally shaped by his engagement with the science of his time. In Berkeley's best-known philosophical works, the Principles and Dialogues, he sets up his idealistic system in opposition to the materialist mechanism he finds in Descartes and Locke. In De Motu, Berkeley refines and extends his philosophy of science in the context of a critique of the dynamic accounts of motion offered by Newton and Leibniz. And in Siris, Berkeley's flirtation with neo-Platonism draws inspiration from the fire theory of Boerhaave as well as Newton's aetherial speculations in the Queries of the Optics. In examining Berkeley's critical engagement with the natural philosophy of his time, we will thus improve our understanding of not just his philosophy of science, but of his philosophical corpus as a whole.

Descartes and Boyle were the most influential proponents of strict mechanist accounts of the physical world, accounts which carried with them a distinction between primary and secondary (or sensible) qualities. For both, the distinction is a piece of natural philosophy. Nevertheless the distinction is quite differently articulated, and, especially, differently grounded in the two thinkers. For Descartes, reasoned reflection reveals to us that bodies must consist in mere extension and its modifications, and that sensible qualities as we conceive of them based on sense perception can pertain only to the mind. Just how we are supposed to arrive at this realization is, this essay will argue, a deep puzzle that brings us to the basic assumptions of Descartes' metaphysics. For Boyle, by contrast, while reflection can reveal the unique explanatory status of mechanism, and, thus, the primary/secondary quality distinction, only experience can confirm its truth. Our central focus will be on Descartes, and on the question: How does he intend to remove the sensible qualities from the physical world, how does he strip them from bodies? I will try to show that Descartes has an argument that he takes to show a priori that sensible qualities cannot be attributed to the material world (as foundational qualities, or, as we conceive of them based on sense experience). The argument fails, however, leaving him with at best a partly empirical case for removing the sensible qualities, based on the purported explanatory success of his physics.

George Berkeley, Bishop of Cloyne, was one of the great philosophers of the early modern period. He was a brilliant critic of his predecessors, particularly Descartes, Malebranche, and Locke. He was a talented metaphysician famous for defending idealism, that is, the view that reality consists exclusively of minds and their ideas. Berkeley's system, while it strikes many as counter intuitive, is strong and flexible enough to counter most objections. His most studied works, the Treatise Concerning the Principles of Human Knowledge Principles, for short) and Three Dialogues between Hylas and Philonous Dialogues), are beautifully written and dense with the sort of arguments that delight contemporary philosophers. He was also a wide ranging thinker with interests in religion (which were fundamental to his philosophical motivations), the psychology of vision, mathematics, physics, morals, economics, and medicine. Although many of Berkeley's first readers greeted him with incomprehension, he influenced both Hume and Kant, and is much read (if little followed) in our own day.

That corpuscularianism played a critical role in Locke’s philosophical thought has perhaps now attained the status of a truism. In particular, it is universally acknowledged that the primary/secondary quality distinction and the conception of real essence found in the Essay Concerning Human Understanding cannot be understood apart from the corpuscularian science of Locke’s time.1 When Locke provides lists of the primary qualities of bodies,2 the qualities that “are really in them whether we perceive them or no,” those lists show strong resemblances to Robert Boyle’s views about the “primary affections” of matter, as expressed in such influential programmatic works as On the Origin of Forms and Qualities.3 Moreover, Locke’s conception of the real essences of bodies, the inner constitutions which serve as the causal sources of all their properties, typically appears to be a corpuscularian one.4 Nevertheless, the question of the nature of Locke’s philosophical allegiance to corpuscularianism remains a controversial one.5..