Plato Timaeus 51

So likewise it is right that the substance which is to be fitted to receive frequently over its whole extent the copies of all things intelligible and eternal should itself, of its own nature, be void of all the forms. Wherefore, let us not speak of her that is the Mother and Receptacle of this generated world, which is perceptible by sight and all the senses, by the name of earth or air or fire or water, or any aggregates or constituents thereof: rather, if we describe her as a Kind invisible and unshaped, all-receptive, and in some most perplexing and most baffling way partaking of the intelligible, 51b we shall describe her truly.
  In so far as it is possible to arrive at the nature of this kind from the foregoing account, one may state it most correctly in this way. That part of it which is made fiery appears each time as fire, that which has been liquefied as water; and it appears as earth and air in so far as it receives copies of these. But let us investigate the matter by more exact reasoning, and consider this question. Does there exist any self-subsisting fire 51c or any of those other objects which we likewise term self-subsisting realities? Or is it only these things which we see, or otherwise perceive by means of bodily senses, that exist, possessed of sensible reality; beside which no other things exist anywhere or anyhow, and it is merely an idle assertion of ours that there always exists an intelligible Form of every object, whereas it is really nothing more than a verbal phrase? Now, on the one hand, it would be improper to dismiss the question before us without a trial and a verdict, and simply to asseverate that the fact is so; while, on the other hand, we ought not to burden a lengthy discourse with another subsidiary argument. 51d If, however, it were possible to disclose briefly some main determining principle, that would best serve our purpose.
  This, then, is the view for which I, for my part, cast my vote. If Reason and True Opinion are two distinct Kinds, most certainly these self-subsisting Forms do exist, imperceptible by our senses, and objects of Reason only; whereas if, as appears to some, True Opinion differs in naught from Reason, then, on the contrary, all the things which we perceive by our bodily senses must be judged to be most stable. 51e Now these two Kinds must be declared to be two, because they have come into existence separately and are unlike in condition. For the one of them arises in us by teaching, the other by persuasion; and the one is always in company with true reasoning, whereas the other is irrational; and the one is immovable by persuasion, whereas the other is alterable by persuasion; and of the one we must assert that every man partakes, but of Reason only the gods and but a small class of men.