Kant’s Aethereal Hammer: When Everything Looks Like a Nail

Throughout Immanuel Kant's works on natural philosophy, he utilizes an omnipresent aether to explain a wide variety of physical events: including optical, thermodynamical, chemical, and magnetic phenomena. Kant even went as far as claiming that the existence of an omnipresent physical aether can be deduced a priori (without appeal to experience, observation, or experiment), in the notorious “aether proof” of his Opus postumum. In retrospect, these commitments are widely seen as a blunder, especially after the demise of the luminiferous aether at the turn of the 20th century. In this paper, I situate Kant's theory of the aether in the context of the physics of his day. I show that, contra the common understanding of the Scientific Revolution, the 17th and 18th centuries witnessed a staggering proliferation of aethereal explanations in natural philosophy: those appealing to subtle substances as causal grounds for classes of physical phenomena. Kant was a part of this tradition in physics, and his aether theory was no embarrassment but rather revealed a keen understanding both of coeval aethereal theories and their shortcomings.