That There are Incorporeal Substances (Abu Rida 1950, 265–69, Adamson and Pormann 2009) is a creative application of ideas from Aristotle’s Categories to the problem of showing that the human soul is an immaterial substance. Al-Kindi takes up this task in stages, first proving that the soul is a substance, then showing that it is immaterial. He argues that the soul is a substance by drawing on the opening chapters of the Categories to claim that the essence of something shares a name and definit