  If this interpretation is right, the message of the one river fragment, B12, is not that all things are changing so that we cannot encounter them twice, but something much more subtle and profound. It is that some things stay the same only by changing. One kind of long-lasting material reality exists by virtue of constant turnover in its constituent matter. Here constancy and change are not opposed but inextricably connected. A human body could be understood in precisely the same way, as living and continuing by virtue of constant metabolism–as Aristotle for instance later understood it.  On this reading, Heraclitus believes in flux, but not as destructive of constancy; rather it is, paradoxically, a necessary condition of constancy, at least in some cases (and arguably in all). In general, at least in some exemplary cases, high-level structures supervene on low-level material flux. The Platonic reading still has advocates (e.g. Tarán 1999), but it is no longer the only reading of Heraclitus advocated by scholars.