(Heraclitus, Fragment B 16)

He is called "the Obscure," ὁ Σκοτεινός. Heraclitus had this reputation even when his writings were preserved intact. Today we know only fragments of his work. Later thinkers—Plato and Aristotle; subsequent authors and philosophical scholars—Theophrastus, Sextus Empiricus, Diogenes Laertius, and Plutarch; even Church Fathers—Hippolytus, Clement of Alexandria, and Origen—all cite passages from Heraclitus here and there in their own works. Thanks to research in philology and history of philosophy, these quotations have been collected as fragments. Sometimes the fragments comprise several sentences, sometimes only one sentence, and occasionally they consist of mere phrases or isolated words.

The train of thought of these later thinkers and writers determines their selection and arrangement of Heraclitus' words. This in turn delimits the space available for any interpretation of them. Thus a closer examination of their place of origin in the writings of subsequent authors yields only the context into which the quotation has been placed, not the Heraclitean context from which it was taken. The quotations and the sources, taken together, sail do not yield what is essential: the definitive, all-articulating unity of the inner structure of Heraclitus' writing. Only a constantly advancing insight into this structure will reveal the point from which the individual fragments are speaking, and in what sense each of them, as a saying, must be heard. Because we can scarcely surmise what the well-spring is that gives the writing of Heraclitus its unity, and because we find this source so difficult to think, we are justified in calling this thinker "the Obscure."