 Unity has a history as well as a logic. Different formulations and debates express intellectual and other resources and interests in different contexts. Questions about unity belong partly in a tradition of thought that can be traced back to pre-Socratic Greek cosmology, in particular to the preoccupation with the question of the One and the Many. In what senses are the world and, as a result, our knowledge of it one? A number of representations of the world in terms of a few simple constituents that were considered fundamental emerged: Parmenides’ static substance, Heraclitus’ flux of becoming, Empedocles’ four elements, Democritus’ atoms, or Pythagoras’ numbers, Plato’s forms, and Aristotle’s categories. The underlying question of the unity of our types of knowledge was explicitly addressed by Plato in the Sophist as follows: “Knowledge also is surely one, but each part of it that commands a certain field is marked off and given a special name proper to itself. Hence language recognizes many arts and many forms of knowledge” (Sophist, 257c). Aristotle asserted in On the Heavens that knowledge concerns what is primary, and different “sciences” know different kinds of causes; it is metaphysics that comes to provide knowledge of the underlying kind.