The present paper first suggests that Quine’s theory of river stage can be used in order to clarify Heraclitus’ concept of the same river. However, in order for Quine’s theory to be useful, it is necessary to have a proper understanding of the principle of individuation. The author then attempts to offer an interpretation of the principle of individuation by means of the principle of abstraction. Finally, Leibniz’s law is discussed through an analysis of the logical behavior of identity.