This chapter considers why “ousia” is the first and most important of Aristotle’s “categories” and is a key concept for his philosophy. It signifies a “being” or “substance,” with “substance” being usefully broad as a term so as to allow a consideration of what any something is. The sorites problem is unpacked to explore this situation. Aristotle compares a heap of sand (sōros), a human being (ousia), and the Iliad as a structured mass of words (and ideas, images) to consider the fundamental nature of “ousia” or “being.” As entities with identity they each in some sense possess “movement” (kinēsis). Aristotle typically possesses a much wider concept of “movement” than ours. It is the becoming of a being, the movement of a being to its telos, whether this be getting a glass of water or writing the Iliad. For Aristotle, movement is more than just mass in motion. He does not conflate chemical matter with organic mass as does the modern Newtonian position. He both differentiates the organic and non-organic, as we clearly must, but his physics also relates to his biology and explains how the biological is an evolved or derived form of the physical.