Engels on Heraclitus
by Friederich Engels.
When we consider and reflect upon Nature at large or the history of mankind or our own intellectual activity at first we see the picture of an endless entanglement of relations and reactions, permutations and combinations, in which nothing remains what, where, and as it was, but everything moves, changes, comes into being and passes away. We see therefore at first the picture as a whole with its individual parts still more or less kept in the background; we observe the movements, transitions, connections, rather than the things that move, combine, and are connected. This primitive, naive, but intrinsically correct conception of the world is that of ancient Greek philosophy, and was first clearly formulated by Heraclitus: everything is and is not, for everything is fluid, is constantly changing, constantly coming into being and passing away.
Quoted in The dialectic of sex; the case for feminist revolution by Firestone, Shulamith 1970
from Socialism: Utopian and Scientific 1880