How new is experimental philosophy?1 Wasn’t Descartes, whose “mechanical philosophy” aimed to overturn Aristotelianism, really an experimental philosopher? After all, much of his attention was devoted to geometry and optics, and for a period he was revered among scholars as, principally, a sort of mathematical physicist. (That’s why the one reference to him educated people mostly know is in talk of the “Cartesian” coordinates he helped invent.) He also spent much time and energy dissecting cows and other animals. Only later was he repositioned as, centrally, a theorist of mind and knowledge, whose primary concern had to do with the justification of belief. In The Passions of the Soul (1649), Descartes aimed to solve what we now think of as the canonically philosophical puzzle about the relation between the soul and the body by way of an empirical hypothesis about the role of the pineal gland. Without the pineal–as Nicolaus Steno pointed out in 1669–Descartes has no story of how mind and body are functionally integrated.2
I don’t want to overstate the case: before the disciplinary rise of modern philosophy, one can readily trace distinctions–between, say, reason and experience, speculation and experiment– that seem cognate to our way of organizing knowledge. Descartes gives us hope when he refers to “first philosophy,” and he famously maintained that “all philosophy is like a tree, of which the roots are metaphysics, the trunk is physics, and the branches, which grow from this trunk, are all of the other sciences, which is to say medicine, mechanics, and morals.”3 Yet even here we can see that his taxonomy isn’t quite ours: morals, to us a division of philosophy, is to Descartes a practical endeavor on a par with medicine.
By the next century, the growing prestige of experimentation was apparent everywhere. The encyclopedist D’Alembert praised Locke for reducing metaphysics to what it should be: la physique expérimentale de l’âme–the experimental science of the spirit. And Hume subtitled his great Treatise of Human Nature, as we don’t always remind ourselves, Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects. The point is not just that the canonical philosophers belong as much to the history of what we now call psychology as to the genealogy of philosophy. It is that the “metaphysical” and the psychological claims are, insofar as we insist on distinguishing them, profoundly interdependent. Their proper place as ancestors of both modern disciplines is reflected in the fact that many of the claims they make about the mind–including those claims that are thought to be of current philosophical relevance–are founded in empirical observation, even if they are not often founded in experiment. They depend on stories about the actual doings of actual people, on claims about how humanity actually is. Hume’s History of England–five volumes of empirical information, elegantly organized– has rightly been seen as expressing philosophical ideas about morality and politics and the human mind. . . .
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