Not only do things change from moment to moment. Even in one and the same moment they are and are not the same. It is not merely that a thing first is, and then a moment afterwards, is not. It both is and is not at the same time. The at-onceness of "is" and "is not" {75} is the meaning of Becoming. We shall understand this better if we contrast it with the Eleatic principle. The Eleatics described all things under two concepts, Being and not-being. Being has, for them, all truth, all reality. Not-being is wholly false and illusory. For Heracleitus both Being and not-being are equally real. The one is as true as the other. Both are true, for both are identical. Becoming is the identity of Being and not-being. For Becoming has only two forms, namely, the arising of things and their passing away, their beginning and their end, their origination and their decease. Perhaps you may think that this is not correct, that there are other forms of change besides origination and decease. A man is born. That is his origination. He dies. That is his decease. Between his birth and his death there are intermediate changes. He grows larger, grows older, grows wiser or more foolish, his hair turns grey. So also the leaf of a tree does not merely come into being and pass out of being. It changes in shape, form, colour. From light green it becomes dark green, and from dark green, yellow. But there is after all nothing in all this except origination and decease, not of the thing itself, but of its qualities. The change from green to yellow is the decease of green colour, the origination of yellow colour. Origination is the passage of not-being into Being. Decease is the passage of Being into not-being. Becoming, then, has in it only the two factors of Being and not-being, and it means the passing of one into the other. But this passage does not mean, for Heracleitus, that at one moment there is Being, and at the next moment not-being. It means that Being and not-being are in everything at one and the same time. Being is {76} not-being. Being has not-being in it. Take as an example the problem of life and death. Ordinarily we think that death is due to external causes, such as accident or disease. We consider that while life lasts, it is what it is, and remains what it is, namely life, unmixed with death, and that it goes on being life until something comes from outside, as it were, in the shape of external causes, and puts an end to it. You may have read Metchnikoff's book "The Nature of Man." In the course of that book he develops this idea. Death, he says, is always due to external causes. Therefore, if we could remove the causes, we could conquer death. The causes of death are mostly disease and accident, for even old age is disease. There is no reason why science should not advance so far as to eliminate disease and accident from life. In that case life might be made immortal, or at any rate, indefinitely prolonged.