Philosophers today have largely given up on the project of categorizing being. Aristotle’s ten categories now strike us as quaint, and no attempt to improve on that effort meets with much interest. Still, no one supposes that reality is smoothly distributed over space. The world at large comes in chunks, and there remains a widespread intuition, even among philosophers, that some of these chunks have a special sort of unity and persistence. These, we tend to suppose, are most truly agents and subjects, and are what exist in the most proper sense of the term. We believe, in other words, in substances.