"Everything flows, nothing stands still"

Heraclitus is recognized as one of the earliest dialectical philosophers with his acknowledgement of the universality of change and development through internal contradictions, as in his statements:

"By cosmic rule, as day yields night, so winter summer, war peace, plenty famine. All things change. Fire penetrates the lump of myrrh, until the joining bodies die and rise again in smoke called incence."

"Men do not know how that which is drawn in different directions harmonises with itself. The harmonious structure of the world depends upon opposite tension like that of the bow and the lyre."

He is famous for expressing the notion that no man can cross the same river twice:

"We both step and do not step in the same rivers.
We are and are not."

The idea of the logos is also credited to him, as he proclaims that everything originates out of the logos. Further, Heraclitus said

"I am as I am not,"

and

"He who hears not me but the logos will say: All is one."

Heraclitus held that an explanation of change was foundational to any theory of nature. This view was strongly opposed by Parmenides, who argued that change is an illusion and that everything is fundamentally static. This promotion of change also led Heraclitus, unusually, to promote warfare and violence, and argue against Homer, as he saw strife as something that led to change:

"War is the father of all and the king of all"
"Every animal is driven to pasture with a blow"

His view on the random chance inherent in the universe is famously the direct opposite of Einstein's:

"Time is a child playing dice; the kingly power is a child's." Heraclitus
"God does not play dice with the universe." Einstein

He appears to have taught by means of small, oracular aphorisms meant to encourage thinking based on natural law and reason. The brevity and elliptical logic of his aphorisms earned Heraclitus the epithet 'Obscure'. The technique, as well as the teaching, is redolent of Zen Buddhism's koans.

Moreover, the Heraclitean emphasis on the nature of things and existence as one of constant change, expressed with language of polarity, is particularly reminiscent of another ancient philosophical tradition, that of Taoism: the Tao (or "the Way") often refers to a space-time sequence, and is similarly expressed with seemingly-contradictory language (e.g., "The Way is like an empty vessel / that may still be drawn from / without ever needing to be filled"). Indeed, parallels may be drawn between the fundamental concepts of the logos (as it was understood during Heraclitus's time) and the Tao.

Heraclitus is described as having a melancholy disposition, and is sometimes referred to as the "weeping philosopher," as opposed to Democritus, who is known as the "laughing philosopher."

There are several legendary stories about Heraclitus, especially concerning his eventual death from illness (and supposed attempt to stave off death using dung and ignoring doctors). These mostly stem from mis-interpretations of the metaphors in his fragments, and an attempt to construct a narrative based on these fragments.