69. All this made it necessary for him to seek out a new primary substance. He wanted not merely something out of which the diversified world we know might conceivably be made, or from which opposites could be “separated out,” but something which of its own nature would pass into everything else, while everything else would pass in turn into it. This he found in Fire, and it is easy to see why, if we consider the phenomenon of combustion, even as it appears to the plain man. The quantity of fire in a flame burning steadily appears to remain the same, the flame seems to be what we call a “thing.” And yet the substance of it is continually changing. It is always passing away in smoke, and its place is always being taken by fresh matter from the fuel that feeds it. This is just what we want. If we regard the world as an “ever-living fire” (fr. 20), we can understand how it is always becoming all things, while all things are always returning to it.[374] Footnote 374: That the Fire of Herakleitos was something on the same level as the “Air” of Anaximenes and not a “symbol,” is clearly implied in such passages as Arist. _Met._ Α, 3. 984 a 5. In support of the view that something different from common fire is meant, Plato, _Crat._ 413 b, is sometimes quoted; but a consideration of the context shows that the passage will not bear this interpretation. Plato is discussing the derivation of δίκαιον from δια-ιόν, and certainly δίκη was a prominent Herakleitean conception, and a good deal that is here said may be the authentic doctrine of the school. Sokrates goes on to complain that when he asks what this is which “goes through” everything, he gets very inconsistent answers. One says it is the sun. Another asks if there is no justice after sunset, and says it is simply fire. A third says it is not fire itself, but the heat which is in fire. A fourth identifies it with Mind. Now all we are entitled to infer from this is that different accounts were given in the Herakleitean school. These were a little less crude than the original doctrine of the master, but for all that not one of them implies anything immaterial or symbolical. The view that it was not fire itself, but Heat, which “passed through” all things, is related to the theory of Herakleitos as Hippo’s Moisture is related to the Water of Thales. It is quite likely, too, that some Herakleiteans attempted to fuse the system of Anaxagoras with their own, just as Diogenes of Apollonia tried to fuse it with that of Anaximenes. We shall see, indeed, that we still have a work in which this attempt is made (p. 167, _n._ 383). [Sidenote: Flux.]