PROBLEMS OF CHANGE AND PERSISTENCE

If everything, without exception, changed completely all the time; if, as Heraclitus believed, everything was in a perpetual flux, there would be no knowledge of the world. Without any permanence even the flux itself could not be conceived as change; there would be nothing in the flux to which we could attribute the differences as changes. We could not even begin to describe such a place: conditions would have become totally different before we could put any description into words. In a Heraclitean universe, science is no more possible than in a Parmenidean universe of complete rest and homogeneity. For there to be a consistent understanding of physical reality there must be, as Aristotle said, some permanence as well as change. We must recognize as facts of nature both that everything changes and that this happens not to every aspect at the same time and at the same rate, but that it occurs in what remains relatively permanent. Losses and gains of certain features occur in things that persist identically over stretches of time. Things move from place to place and besides, as Aristotle also pointed out, they undergo three other types of change. They change in quantity, alter in their qualities, and are destroyed or come into being. Except for the last type of change, an object remains identical with itself while its attributes or aspects change. In the last type, along with its qualities, the object itself is changed into a different thing. If change is the loss of something (such as a position, a property, etc.) it is also, and almost always, the gain of something new, of the same category as what is lost.