Ether and derivative forces in Kant’s natural philosophy

Debates over the nature, status, and explanatory scope of various ethers were widespread among seventeenth- and eighteenth-century natural philosophers. This article argues that an important feature of Kant's mature natural philosophy is its attempt to combine these issues with the Leibnizian problem of the relation between fundamental and derivative forces. On the one hand, Kant employs the framework of fundamental and derivative forces to structure the disparate phenomena that were at stake in the ether debates. On the other hand, the ether is central to his explanation of the relation between fundamental and derivative forces. After examining the relevant texts and surveying different interpretative options, the article argues that Kant favours an ether-based account of the relationship between fundamental and derivative forces. The account is fleshed out through the case of cohesive force, which I show to be an effect not of the pressure of the ether but of differences in its oscillatory motion.