How air and water take part in forming rock in the Timaeus

Plato (c. 428/427–348/347 BCE), a Greek philosopher from Athens, gives the speaker Timaeus the task of explaining the constitution of the visible world. As his account turns to the different kinds of earth, an ordinary experience comes into view. Water dissolves or carries away some earthy substances. The same treatment appears to achieve very little against a piece of solid rock. How can materials with a common beginning offer such different degrees of resistance?

What happens in the spaces

Thus earth, when compressed by air into a mass that will not dissolve in water, forms stone; of which the transparent sort made of equal and uniform particles is fairer, while that of the opposite kind is less fair.

– Plato, Timaeus, 1888, p. 219.^[1]

Timaeus directs attention towards what happens between the particles of earth. Water belongs to their history. When it leaves, the arrangement of what remains changes. The surrounding air also has an active part in the account. It bears upon the earth and presses the particles together. The solid piece eventually taken up by an observer is thus understood to contain the outcome of a succession of movements.

Explaining the resistance of rock

Water serves once more as a measure of the firmness attained. Can it separate the compacted earth, or will that earth hold together? This gives a reader a concrete way into a subtle distinction. One need never have seen the interior of a stone to understand the question Timaeus means to ask. It is enough to remember the difference between a patch of ground turned to mud and a wall of rock. The speaker leads from that familiar contrast towards the unseen spaces and pressures through which he hopes to account for it.