- Whence the Chemistry of Hume's Mind?
Reading Tamás Demeter's recent book, "David Hume and the Culture of Scottish Newtonianism," feels like visiting a curiosity shop. There are some general themes that are meant to harmonize the work, such as the emphasis on the conceptual and methodological unity of natural and moral philosophy. This merging of cultures of inquiry is nicely illustrated with the case study of anger in the period. There is the main thesis: that Hume's science of mind was influenced, not as much by Newton's Principia, as by Newton's Opticks. Newton's Opticks informs the "sciences of quality," such as chemistry and physiology in eighteenth-century Scotland, and then chemical and anatomical thinking makes its way to Hume's science of mind. These discussions are often fascinating, and long-standing readers of Hume will be delighted to find Hume in this fresh intellectual landscape. Here Hume joins remarkable figures like George Cheney, William Cullen, William Porterfield, and other instrumental "vitalist" thinkers who, inspired by Newton's Opticks, developed new conceptual tools for theorizing about natural phenomena that resisted the rigorous mathematization and mechanization of the dominant Principia-style culture of science. [End Page 241]
Like a curiosity shop, the book displays its items or themes in a somewhat haphazard manner, and connections are often hinted at rather than established. I did, however, discern in Demeter's book a philosophical hidden gem. "Hume's chemistry," a permanent new term in my vocabulary, is indeed, I believe, a philosophical diamond in the rough, one that has the potential to change in important ways how we understand some of Hume's most controversial claims.
It seems to me that it is Hume's "chemical thinking" that sends Demeter in the directions we witness in the book, although the subject of Hume's chemistry appears rather late, when Demeter discusses a number of passages, mostly from Hume's discussion of the passions in Book 2 of the Treatise. Reading these passages as Demeter collects them made it vividly obvious to me, for the first time, that there is an important phenomenon that deserves to be labeled and studied: the chemistry in Hume's mind. Here are some of the passages that struck me with particular force (I leave my favorite for the end).
Are not these as plain proofs, that the passions of fear and hope are mixtures of grief and joy, as in optics 'tis a proof, that a colour'd ray of the sun passing thro' a prism, is a composition of two others, when, as you diminish or encrease the quantity of either, you find it prevail proportionably more or less in the composition? I am sure neither natural nor moral philosophy admits of stronger proofs.(T 184.108.40.206; SBN 443–44)
I fancy this passage to be the reactant, the element that sets off the reaction that turns into Demeter's book. What is the significance of Hume's startling comparison of the passions with the phenomenon of the prism that so occupies Newton in the Opticks? Elsewhere Hume depicts "hope and fear" as arising "from the different mixture of these opposite passions of grief and joy, and from their imperfect union and conjunction." (T 220.127.116.11; SBN 442–43). How much did Hume grasp of chemistry? What did anyone in the time know about chemistry? How exactly did Hume imagine that mental phenomena behaved like "chemical preparations, where the mixture of two clear and transparent liquids produces a third, which is opaque and colour'd" (T 18.104.22.168; SBN 452)?
Most fundamentally, chemistry is about the qualitative novelty referred to in this passage from T 22.214.171.124 (SBN 452). You mix two clear and transparent liquids and it produces a third liquid that is opaque and colored. The third liquid has a reality that is lacking in its constituents. Hume obviously considers the passions to behave in this way. But how far...