Since some things are such as to come-to-be and pass-away, and since coming-to-be in fact occurs in the region about the centre, we must explain the number and the nature of the ‘originative sources’ of all coming-to-be alike: for a grasp of the true theory of any universal facilitates the understanding of its specific forms.

The ‘originative sources’, then, of the things which come-to-be are equal in number to, and identical in kind with, those in the sphere of the eternal and primary things. For there is one in the sense of ‘matter’, and a second in the sense of ‘form’: and, in addition, the third ‘originative source’ must be present as well. For the two first are not sufficient to bring things into being, any more than they are adequate to account for the primary things.

Now cause, in the sense of material origin, for the things which are such as to come-to-be is ‘that which can be-and-not-be’: and this is identical with’that which can come-to-be-and-pass-away’, since the latter, while it is at one time, at another time is not. (For whereas some things are of necessity, viz. the eternal things, others of necessity are not. And of these two sets of things, since they cannot diverge from the necessity of their nature, it is impossible for the first not to he and impossible for the second to he. Other things, however, can both be and not he.) Hence coming-to-be and passing-away must occur within the field of ‘that which can be-and not-be’. This, therefore, is cause in the sense of material origin for the things which are such as to come-to-be; while cause, in the sense of their ‘end’, is their ‘figure’ or ‘form’-and that is the formula expressing the essential nature of each of them.

But the third ‘originative source’ must be present as well-the cause vaguely dreamed of by all our predecessors, definitely stated by none of them. On the contrary (a) some amongst them thought the nature of ‘the Forms’ was adequate to account for coming-to-be. Thus Socrates in the Phaedo first blames everybody else for having given no explanation; and then lays it down; that ‘some things are Forms, others Participants in the Forms’, and that ‘while a thing is said to “be” in virtue of the Form, it is said to “come-to-be” qua sharing in,” to “pass-away” qua “losing,” the ‘Form’. Hence he thinks that ‘assuming the truth of these theses, the Forms must be causes both of coming-to-be and of passing-away’. On the other hand (b) there were others who thought ‘the matter’ was adequate by itself to account for coming-to-b............