variously expressed as ‘nothing can come out of nothing or ‘the existent cannot come out of the non-existent, or the non-existent out of the existent.’ This axiom, as understood by those who accepted it, Aristotle regards as false. The deductions they made from it, so far as they were seriously accepted, flatly contradicted Nature, and also led to internally self-contradictory conclusions; or at the very least, tended to divert attention from the true problem and from fruitful attempts to deal with it.

Parmenides and his disciples, according to Aristotle, clearly saw that their axiom amounted to a blank contradiction of all change and movement, and so to a conception of Nature as unitary and rigidly unchanging and undifferentiated. They granted that ‘appearances’ contradict this; that is so much the worse for the appearances. They contradict the truth and therefore do not exist at all, but only ‘appear’ to do so.

Others were less consistent, but as they too held it to be impossible for anything to come out of nothing, the question that chiefly interested them was not’ How are we to regard change, and how investigate changes? ‘but’ What are we to suppose it is that is always there in reality, while it appears as if everything were passing in and out of existence?’ It is really all air, said one; all water, said another; the four elements, said a third; every known substance or tissue out of which things are visibly built up by addition and interlacing, said another. Thus they were all of them looking for the ‘existent,’ i.e. the reality (as distinct from appearance) which never comes to be or ceases to be, but is ‘always there.’ This, however, was not examining the fact of change (which is the distinctive characteristic of what we mean by Nature) at all. It simply diverted the mind from it. And, obscurely feeling this in spite of themselves, all the thinkers (even including Parmenides himself, when he deigns to look at ‘appearances’) had recourse to certain agents of change, which they brought in under the guise of’ contrasted principles,’ such as ‘hot and cold,’ or ‘more and less,’ and so forth, between which, as between two poles, change takes



place—or seems to do so. Obviously, then, it is here that we must look for the tracks of that driving force of the truth that secretly diverted them from the lines they were trying to follow, and lured them into an undesigned accord with Nature, and so with each other, even where they were most conscious of mutual opposition.

Thus at last we come to the right questions, and ask: What conceptual analysis of the observed process of change will give us the best starting-point for clear thinking and fruitful observation? What and how many are the factors or constituents of change? What technical terms give best promise of precision and accuracy?

Aristotle tries a variety of formulae and compares their merits, always keeping steadily in view the passage of the changing thing from one state to another. He notes a certain goalfulness in Nature, analogous to our own purposeful actions. He sees that, if we follow any definite series of changes, such as that from the acorn to the oak, we find that at every stage of progress the changing thing lacks something of the thing it is to be, and this ‘shortage’ is an essential characteristic of what, at the moment, it already is: and this provokes interesting reflections as to the relation of the ‘existent or non-existent’ philosophy to these ‘absences’ or ‘shortages,’ which are negative yet definite. Are they existent or non-existent? What is this ‘not-yet-there-ness’ (which, under a more positive aspect, we call a’ potentiality’) that goes shares with ‘already-there-ness’ in the ceaseless ‘becomings’ of Nature?

DOI: 10.4159/DLCL.aristotle-physics.1957