Notice that the transformations are cyclical. When they are complete, what started as fire ends up being fire again.
Now, two questions naturally arise about this cycle of transformations: What causes it to occur? And what happens to fire, for example, when it becomes air? Anaximander’s answer to the first question is that strife between the opposites causes the transformations on Road A (the downward road), and that justice causes the transformations on Road B (the upward road). Heraclitus adopts this answer, but sees that it can be simplified without loss of explanatory power. He sees that because the transformations are cyclical, we do not need two forces—strife and justice—to drive them, but only one. Hence he tells us that “justice is strife,” that “the road up and the road down are one and the same,” and that “the beginning and end are common on the circumference of a circle.” Thus the force that transforms fire into air also transforms air back into fire. (This Heraclitean criticism of Anaximander is a model of critical scientific rationality at work. Physicists like Steven Weinberg or Murray Gell-Mann, who look for Grand Unified Theories in which gravitational, electromagnetic, and weak and strong forces are unified, are heirs to Heraclitus.)
To see how Heraclitus answered the question about what happens to fire when strife causes it to become air, we must begin, as he surely did, with Anaximenes. In Anaximenes’ view, elements change into one another by becoming more rarified or more condensed. But this account is uneconomical because it introduces a new primitive notion—rarifaction/condensation—over and above the original four elements. Heraclitus seems to have noticed this defect in Anaximenes’ theory and tried to rectify it. In his view, all that happens when fire is transformed into air is that it dies down. Thus Road A (the downward road) is the progressive dying down of fire and Road B (the upward one) is its progressive rekindling. Thus only fire “being kindled in measures and being extinguished in measures,” is needed to explain how strife (justice) causes the elements to be transformed into one another, so that their cyclical transformations are simply “the turnings of fire.”
But why does Heraclitus assign such a fundamental role to fire rather than to air or one of the other elements? Why does he identify the cosmos with “ever-living fire” rather than with ever-living air or ever-living water? Why is Road A the progressive dying down of fire rather than the progressive drying of the wet? To see a possible answer, we need to return to the first question we raised: What causes the elements to be transformed into one another? Anaximander’s answer was strife and justice. Heraclitus simplifies this to a single causal agent: strife. But Anaximander does not tell us why the elements strive with one another in the first place. Strife enters the Anaximandrian cosmos, as it were, from the outside; it is something extrinsic to, or over and above, the unlimited and the four elements. Strife, however, is intrinsic to a cosmos of fire. For fire is “want and satiety”: it exists only when striving with what it is trying to burn; it simultaneously wants or needs fuel and is becoming hungry through consuming it. It is this dynamic feature, possessed by none of the other opposites, that most likely led Heraclitus to assign priority to it. It enables him to “reduce” strife to fire (since if fire exists so must strife) just as he has already reduced justice to strife.
One final theoretical advantage of fire deserves to be mentioned. Fire exists through striving with its fuel, but its striving is law-governed or measured:
Earth is poured out as sea, and is measured according to the same ratio (logos) it was before it became earth.
After all, the size or heat of fire is proportional to the amount of fuel being consumed. Thus if fire is the fundamentally real thing, this offers an explanation of the order observed in such things as the seasons and the rising and setting of the sun.
There is no doubt that the theory that results from these reductions is vastly more successful than any of the theories of Heraclitus’ predecessors. It is also fundamentally different in kind. Heraclitus doesn’t tell us that the cosmos and all its contents are fundamentally fire, he tells us that they are fire “being kindled in measures and being extinguished in measures.” This emphasizes the fact that what is fundamentally real for Heraclitus is not a static stuff to which change and activity are extrinsic, but a law-governed process or activity. Heraclitus differs from his predecessors, then, not simply in choosing fire rather than water, air, or the unlimited as his primary stuff, but in choosing law-governed change over static stability as being more fundamentally real. In the worlds of Thales, Anaximander, and Anaximenes, change depends on stability; in Heraclitus’ world, stability depends on change: “Changing, it rests.”
Heraclitus’ powerful vision of the world exerted enormous influence over his successors, who tried in various ways to destroy, criticize, modify, and augment it. But it is not his theory so much as the spirit in which he offers it, that I have wanted to emphasize. He wasn’t the first to theorize in that spirit, he was part of a tradition of critical rationality that already existed. But he was the first to give explicit voice to it:
Listening not to me but to the logos it is wise to agree that all things are one.
This is the injunction that all the subsequent Greek philosophers follow. As students of Greek philosophy, it is an injunction we must strive to follow ourselves. If we do, we will become what so many Greek philosophers thought was the best thing to be: critically rational human beings.
These classic Hum lectures were selected by Peter Steinberger [political science and humanities 1977–].
Patricia Curd, ed., A Presocratics Reader (Indianapolis: Hackett, 1996)
Charles Kahn, The Art and Thought of Heraclitus (Cambridge: Cambridge University Press, 1979)
Karl Popper, “Back to the Presocratics,” in his Conjectures and Refutations (London: Routledge, 1963)