Having chosen his ground carefully, Hobbes launches an epistemological attack on metaphysics. The academic philosophers had arrived at the Theory of Matter and Form from consideration of certain natural paradoxes subsumed under the general heading of the Unity Problem. For example, a body appears to be one thing and yet it is distributed into many parts. Which is it, one or many? Aristotle had arrived at the real distinction between matter and form, metaphysical components whose interpenetration produces the paradox. The whole unity comes from the substantial form and the distribution into parts from the matter. Inhering in the parts giving them really distinct unities are the accidental forms. The unity of the whole being is actuated by another really distinct principle, the existence.