During his lifetime, Heraclitus of Ephesus thought about ethics, cosmology, and the nature of being. He used paradoxes to point out the complexities involved in conceiving the nature of reality. These paradoxes show that the plurality of things are in some way united. Sometimes his statements seem contradictory at first, but they may in fact point to logical inferences which could resolve the contradiction. For example, he says that "An unapparent connection (harmonia) is stronger than an apparent one" (Curd, 45). If the apparent is what is material and visible, then the form, which is intelligible but not visible, could be the unapparent unifying factor in the connection.
Indeed, Heraclitus states that "What is opposed brings together; the finest harmony is composed of things at variance, and everything comes to be in accordance with strife" (Curd, 47). Unity consists of elements in tension held together by a single overarching form. This is as true of an artwork as it is of a tree. The branches, roots, leaves, and trunk present a plurality of things held in unity by the form of the whole tree. This is not a Platonic form, but rather the sort of form that an artist imposes onto marble. The tension in the Laocoon Group comprises a single form. Similarly, the tension from the centrifugal motion of planets and the gravity of the sun results in a unified system. While Heraclitus would not have known these particular examples, they seem adequate for describing the sort of unity about which he was thinking.
Moreover, Heraclitus reflects on the nature of being. He says, "We step into and we do not step into the same rivers. We are and we are not" (Curd, 45). He seems to mean that things which are changing exist in a perpetual state of flux. While I certainly exist, I am not the same now as I was when I began writing this sentence. I am always changing, but there seems to be something intelligible that does not change. Otherwise I would have to introduce myself anew each day, and we would also be unable to name rivers.
Indeed, He says that "This kosmos, the same for all, none of gods nor humans made, but it is always and is and shall be: an ever-living fire, kindled in measures and extinguished in measures" (Curd, 45). The cosmos, like fire, is perpetually in a state of flux. It comes into being and goes out of being continually. Perhaps this is why he says that "Changing it rests" (Curd, 46). One of the unchanging rules of the cosmos, it seems, is that it continually changes. By saying that the cosmos is always changing, Heraclitus also is stating that the cosmos has unchanging principles.
Heraclitus uses paradoxes to highlight the underlying nature of things. He posits that tension and unity occur simultaneously, and he seems to think that the cosmos is constantly changing. These theories seem to be self-contradictory, but they are explainable. However, this requires some inference from Heraclitus' own words. Even so, he offers very accurate insights into the nature of the world in which we live.