 The last two paragraphs have helped to clarify appetition. It is time to return to perception. In Leibniz’s definition (the expression of the many in the one) the two key terms are “expression” and “one.” Both of them bear considerable weight in Leibniz’s metaphysics. Representation or expression (Leibniz uses the two terms interchangeably) has its own definition: “One thing expresses another … when there is a constant and regulated relation between what can be said of the one and of the other” (letter to Arnauld, 9 October 1687; G II, 112/LA 144). Examples, in addition to perception, include a map expressing or representing a geographical region and an algebraic equation representing or expressing a geometric figure, such as a circle or an ellipse.