The Two Clocks Relation is a hypothetical teleological instance used to support theories of quintessential matter and natural harmony in the Universe.

It is most frequently used to explicate Gottfried Leibniz's theory of monadic existence, a pseudo-spiritualistic position that asserts that there is no difference between the intellect and matter, because everything that is perceived by people as matter is in fact consistent of spiritual quanta called "monads" (and, during Leibniz's time, "intellect" was considered by most to be purely spiritual). Monads, Leibniz said, do not have any physical properties, and do not interact with each other dimensionally, and that people perceive material interaction because the monads that they consist of are harmonized with the monads of other materials so as to produce the understanding of interaction. The only way Leibniz could maintain these far-fetched claims was by legitimizing the harmony of the monads that make everything in the Universe up. Nowadays, Leibniz's method of doing so is explicated with the "Two Clocks Relation".

Leibniz's legitimization was very simple: He claimed that because all existents in the Universe were produced immediately by God that they are all essentially identical expressions, and that they therefore all have precisely the same properties. The only differentiation in that which is perceived to be matter is how and when the monads exist in relation to each other, i.e. whether a cluster of monads forms, by coincidence, a person or a stone. Leibniz certified, however, that regardless of what those monads form, they should maintain their individuality forever, such that each monad, regardless of its state or position, should change only in concordance to every other existent monad. This legitimization is characterized as a "Two Clocks Relation" because it is approximately congruous to the observable concordance of two perfect timepieces that are set at the same time; for as long as they remain perfect (as the monads are, as nonreactive products of God), they should forever be in harmony, acting together without aberration.

The only source for this article is Bertrand Russel's "The History of Western Philosophy."