Kant had a lot in common with the Swedish mystic. He, too, was a northern European, a Protestant, and a man of science. At a time when philosophy and “natural philosophy”—the scholarly pursuits that developed into today’s natural sciences—were not yet entirely separate, Kant published work not only about metaphysics and ethics but also about physics, cosmology, and earthquakes. In his first book, “Thoughts on the True Estimation of Living Forces,” published in 1749, Kant wondered how the human body, which is entirely material and physical, is related to the human mind, which doesn’t seem to be. “How is it possible for a force that produces only motions to generate representations and ideas?” he asked.