Their importance consists in the evidence they yield of cultivated thought about nature before it had been forced into a uniform mould by the long tradition of scientific philosophy.

For example in the _Timaeus_ there is a presupposition, somewhat vaguely expressed, of a distinction between the general becoming of nature and the measurable time of nature.

In a later lecture I have to distinguish between what I call the passage of nature and particular time-systems which exhibit certain characteristics of that passage.

I will not go so far as to claim Plato in direct support of this doctrine, but I do think that the sections of the _Timaeus_ which deal with time become clearer if my distinction is admitted.
This is however a digression.

I am now concerned with the origin of the scientific doctrine of matter in Greek thought.