HERACLITUS

The Greek philosopher Heraclitus (540 B.C. - 460 B.C.) attempted to explain the nature of the universe by assuming the existence of the "logos," that is, order or reason, as the unifying principle which guides all things and by specifying fire as the basic substance which underlies physical reality.

He is a solitary figure who claims to have sought the truth within himself, and although his work shows familiarity with the writings of other philosophers, particularly those of Anaximander, both his unique ideas and his peculiar literary style set him apart.

The basis of his philosophy is the world of appearance, the sensible world. He state that "All things are constantly changing, and thus it is impossible to step into the same stream twice." Change is due to the mutual resolution of opposites such as hot and cold, day and night, hunger and satiety, although underlying all change and guiding it is a basic unity expressed by the idea of the logos. He also believed that that which seems to be at variance with itself through conflict or tension (which is inherently the case with opposites) is in reality expressive of a kind of harmony.

Although the cosmos, in Heraclitus's view, has always existed and therefore did not come into being at some arbitrary point in time, fire, under the influence and guidance of the logos, is the basic substance in it, and all elements are some transformation of it. It is not completely independent but is infused with the logos, as is the human soul, and it is for  this reason that the soul may come to grasp the truth of the cosmos, although human understanding may reach only childish limits.

Heraclitus enjoins men to learn the nature of the universe through an understanding of their own souls and has been considered as the first mental philosopher. Exact language and thought are of paramount importance to him, since he conceives of the logos as both the underlying order in the cosmos and the soul's verbal expression about it.

He is important as one of the first Greek philosophers to take up the problem of knowledge, and he is undoubtedly the first to stress the importance of an understanding of the soul as a step toward understanding the external world order. Here, soul means the animating and vital principle in humans, credited with the faculties of thought, action, and emotion and conceived as an immaterial entity. The writings of Heraclitus provided much of the theoretical basis for Stoicism.