Timaeus

Therefore, by assigning this form to earth, we preserve the probable account; and further, to water, we assign the most immobile form among the remaining ones, the most mobile to fire, and the middle one to air. Also, the smallest body to fire, the largest to water, and the middle one to air; and further, the sharpest to fire, the second to air, and the third to water. Now all these things: that which has the fewest bases must of necessity be the most mobile, being the most cutting and the sharpest in every way of all, and also the lightest, as being constructed from the fewest of the same parts; and the second must have these same properties in the second degree, and the third in the third degree. Let, then, according to correct reason and according to probability, the solid form which has become a pyramid be the element and seed of fire; and let us say that the second in order of generation is of air, and the third is of water. Now all these things must be conceived as being so small that single ones of each class, because of their smallness, are not seen by us at all, but when many are gathered together, their bulks are seen. And indeed, with respect to the proportions of their numbers, motions, and other powers, god, in every way, insofar as the nature of necessity yielded willingly and under persuasion, harmonized these things in proportion, they being completed by him in all accuracy. From all those whose classes we have previously mentioned, the matter would most probably stand as follows. When earth meets with fire and is dissolved by its sharpness, it would drift about, whether dissolved in fire itself, or in a mass of air, or of water, until its parts, meeting somewhere, fit together again with one another and become earth once more—for it would never pass into another form—while water, when divided by fire or even by air, can become, by being reconstructed, one body of fire and two of air; and the fragments of air, when a single part is dissolved, would become two bodies of fire. And again, when a small amount of fire is enclosed in many others, such as air, waters, or some earth, and moving among those carried along, fighting and being defeated, is broken to pieces, two bodies of fire combine into a single form of air; and when air is mastered and shattered, out of two whole ones and a half, a single whole solid form of water will be composed.

​Timaeus: For let us reason about them again in this way: when some other class, caught in fire, is cut by it, by the sharpness of its angles and along its sides, once it is reconstructed into the nature of fire, it ceases to be cut—for any class which is like and identical with itself is unable either to cause any change in, or to suffer anything from, that which is in the same state and like it—but as long as, in passing into something else, being weaker, it fights against a stronger one, it does not cease to be dissolved. And again, when the smaller bodies, being few and enclosed in many larger ones, are shattered and extinguished, if they are willing to combine into the form of the prevailing one, they cease to be extinguished, and air is generated from fire, and water from air. But if they go into the same places and some other of the coming classes fights against them, they do not cease to be dissolved until either, being utterly thrust out and dissolved, they escape to their kindred, or, being defeated, they become a single thing out of many, like the prevailing one, and remain as a fellow-dweller with it. And indeed, in accordance with these affections, all things change their places; for the multitudes of each class are separated in their own place because of the motion of the receiver, and those which become unlike themselves and like others from time to time are carried, because of the shaking, toward the place of those to which they have become like. Thus, then, the unmixed and primary bodies have been generated through such causes; but as for the existence of different varieties within their classes, we must blame the construction of each of the two elements, because the triangles planted at the beginning were not of one size only for each, but both smaller and larger, having as many sizes as there are varieties within the classes. Therefore, when mixed both with themselves and with one another, they are infinite in their variety; which variety must be observed by those who intend to use a probable account concerning nature. Concerning motion and rest, then, in what manner and in the presence of what things they arise, if one does not come to an agreement, there would be many obstacles to our subsequent reasoning. Now, some things have already been said about them, but in addition to those, there is still this: that motion is never willing to exist in uniformity. For that which is to be moved without that which is to move it, or that which is to move without that which is to be moved, is difficult, or rather impossible, to exist; and there is no motion when these are absent, and it is impossible for these ever to be uniform.