I am researching an iatrochemical (lit.: medical-chemical) movement centered around the Universities of Halle, Jena, and Gotha in early modern Germany where the medical chemists Georg Stahl, Friedrich Hoffmann, and their students practiced. These thinkers and experimenters attempted to find the boundaries between the inorganic (chemical) world and the organic (medical) world and carefully explain how these two systems of causation influenced each other. The result was vitalist theories, which described goal-actions (“I want to raise my arm”) as a special set of natural laws, different from and overlaying the (Newtonian) mechanical laws (“I, a pool-ball, want to recoil when struck”). Indeed, their project was supposed to bear fruit especially insofar as it marked the permeable boundaries between the two and allowed skilled chemists and doctors to traverse that boundary.

I was drawn to work on the philosophy of German medical chemistry in the early 18^th century because it represented an alternate outlook to either mainstream scientific or philosophical worldviews. The history of chemistry and the history of philosophy have lived, for much of the 20^th and 21^st centuries, in an arms-length embrace. It is unavoidably true that 17^th and 18^th century chemistry was much concerned with questions of natural philosophy – the relationship between the soul and the material world, how animals and humans are generated, whether the world works mechanically, like a clock, or by other means – but the answers these early modern chemists come up with often seem strangely off-track from the main thrust of academic philosophy at the time. They were dirtier (both literally; labwork was dark, dirty, and hot; and intellectually; with more loose ends and open questions) and more practically oriented than chemistry, but more abstract and metaphysical than modern (Baconian) science and medicine.

Doing my archival research, I was struck by the extent to which the famous differences between these authors (Hoffmann says he believes only in mechanical causes, Stahl demands vital causes) more resembles a dance than a debate. Close analysis of the sources suggests that their disagreements and similarities were often not as sharp as the authors believed. Instead, they constructed their arguments as relationships to their fellows, building out a multi-layered dance that took only the form of a debate. Especially when it came to putting their ideas into practice, the practical teachings of these thinkers (who were all practicing chemists and medici) contained misunderstandings, corrections, harmonizations, and emendations which do not always appear in their strictly dogmatic claims.

These Halle chemists left a long shadow on the histories of chemistry, in part by laying the groundwork for Antoine Lavoisier’s oxygen theory, as well as on the history of philosophy (Immanuel Kant claimed Stahl had been one of his greatest influences). However, I would suggest that it is in the field of psychology that the Halle chemists are most useful. They provide us with a model for how to bravely attempt to overcome our simple reductionist frameworks of physicalism (a type of mechanism) and dualism (a stringent divide between the mental and the physical) and think in new ways about both the mechanical and the intentional to conceive of them as being mutually supporting ways of seeing the natural world.