Platonic causality

Reading on into the Phaedo, we get to Socrates' exposition of causality.

There is nothing new, [Socrates] said, in what I am about to tell you; but only what I have been always and everywhere repeating in the previous discussion and on other occasions: I want to show you the nature of that cause which has occupied my thoughts, and I shall have to go back to those familiar words which are in the mouth of everyone, and first of all assume that there is an absolute beauty and goodness and greatness, and the like; grant me this, and I hope to be able to show you the nature of the cause, and to prove the immortality of the soul.

Cebes said: You may proceed at once with the proof, as I readily grant you this.

Well, he said, then I should like to know whether you agree with me in the next step; for I cannot help thinking that if there be anything beautiful other than absolute beauty, that can only be beautiful in as far as it partakes of absolute beauty - and this I should say of everything. Do you agree in this notion of the cause?

Yes, he said, I agree.

He proceeded: I know nothing and can understand nothing of any other of those wise causes which are alleged; and if a person says to me that the bloom of color, or form, or anything else of that sort is a source of beauty, I leave all that, which is only confusing to me, and simply and singly, and perhaps foolishly, hold and am assured in my own mind that nothing makes a thing beautiful but the presence and participation of beauty in whatever way or manner obtained; for as to the manner I am uncertain, but I stoutly contend that by beauty all beautiful things become beautiful. That appears to me to be the only safe answer that I can give, either to myself or to any other, and to that I cling, in the persuasion that I shall never be overthrown, and that I may safely answer to myself or any other that by beauty beautiful things become beautiful.

(Plato, Phaedo:100b-e)

So something is only insofar as it partakes of its Eidos i.e., Essence or Form. Put another way, the causes of the phenomena that appear to our senses are their Essences. This provides an account of generative, ontological, causality but what about the more mundane occurrences of cause and effect such as melting ice by applying heat?

There is a thing which you term heat, and another thing which you term cold?

Certainly.

But are they the same as fire and snow?

Most assuredly not.

Heat is not the same as fire, nor is cold the same as snow?

No.

And yet you will surely admit that when snow, as before said, is under the influence of heat, they will not remain snow and heat; but at the advance of the heat the snow will either retire or perish?

Very true, he replied.

And the fire too at the advance of the cold will either retire or perish; and when the fire is under the influence of the cold, they will not remain, as before, fire and cold.

That is true, he said.

(Plato, Phaedo:103c-d)

So ice becomes water when its 'iceness' retires at the advance of heat and it presumably partakes in 'waterness' in its stead. Therefore, causality does not, and cannot, occur amongst Essences because they never change but their relationships between each other and the phenomena in which they are instantiated are defined such that causality is merely the appearance of a phenomenon's changing participation in the immutable Essences.