The earliest recorded philosophical use of the term "phusis" occurs in the fragments of Heraclitus (most notably at B1 and B123). Phusis, in the non-philosophical writings relevant to Heraclitus’s time (e.g. from Homer to Aeschylus and Pindar), was generally used to characterize the external physical appearance of something. Heraclitus, on the other hand, seems to have used the term in the completely opposite manner: an object’s phusis is hidden (kruptesthai) and greater (kreissōn) than the external appearance (B123 and B54). Despite (...) this difference, Heraclitus’s use has an affinity with the common use in his time: phusis is used to characterize things. In B1, for example, Heraclitus makes it clear that he is interested in explaining the nature of each thing as opposed to some cosmic principle of Nature. By examining various fragments, I make the case that the phusis of a thing, for Heraclitus, can be defined as the set of opposites necessarily inherent in an object upon which all objects of that kind depend for their existence. The interesting result is that Heraclitus’s novel use of phusis happens to be the foundation for one of the ways in which opposites form a unity. This particular thesis states that there are essential properties inherent in objects which are pairs of opposites sufficient to determine the unity of the object in question. If this is right, then we can read some fragments which contain descriptions of worldly objects (e.g. bows, lyres, rivers, barley drinks etc.) in a new light. These descriptions of worldly objects might not be meant to stand as metaphoric symbols for cosmic principles, as is often thought; rather, they can be read as instances of Heraclitus attempting to do a metaphysics of objects. (shrink)