Socrates sums up, that motion is beneficial to body and soul, and inaction the opposite. To illustrate, he recalls the image in Homer’s Iliad VIII.17-27, in which Zeus boasts that he could tie up the earth with a golden cord and suspend it from the top of Mount Olympus – thus stopping all the cosmic movements and cycles whose constant motion ensures their survival (153c-d).
From the cosmic to the everyday, Socrates then describes the process of how we see colour. The colour white, he says, isn’t a distinct entity on its own: ‘According to this theory, black or white or any other colour will turn out to have come into being through the impact of the eye upon the appropriate motion’ (ek tēs prosbolēs tȏn ommatōn pros tēn prosēkousan phoran). What we commonly call colour is something between the eye and the stimulus, and is distinctive to each perceiver (154a).
After all, dogs and humans don’t seem to perceive colour in the same way. And a colour can appear different even to the same person on different occasions. We may note that the perennial appeal of optical puzzles – ‘Is the dress green or blue?’ – depends upon their perception being somewhat different for various observers. Objects can feel cold to one observer and warm to another (the same point as made earlier about the breeze), yet we don’t think the object itself has changed. Protagoras himself, Socrates declares, would be the first to zero in on errors of that kind (154b).
On Theaetetus’s call for an explanation here, Socrates gives an example. You have a batch of six dice (Batch A). If you put another batch of four (Batch B) beside it, the first batch is half as large again as the second; but if you put a batch of twelve (Batch C) down too, A is half the size of C. Yet A hasn’t changed in size itself: it’s just less or more in comparison with C or B.
If Protagoras asked Theaetetus if an object could become bigger any other way than being increased, the answer would be no. But Batch A seems, on one view, to have undergone a status change from larger to lesser, and we risk contradicting ourselves. Socrates is, once again, pleased with the young man’s cautious answer, responding with a delightful sketch:
‘Now if you or I were professional wise men (deinoi kai sophoi), who had already analysed all the contents of our minds, we should now spend our superfluous time trying each other out; we should start a regular Sophists’ battle (eis machēn), with a great clashing of argument on argument (tous logous tois logois.) But as it is, we are only ordinary people (idiōtai)’ (154d-e).
Once carefully viewed, it is agreed that nothing can have become either greater or smaller in bulk or in number, as long as it is equal to itself (eōs ison eiē auto heautōi). And for something to change into something else, there must be a process of becoming (155b). Humans, for example, change: they grow from children into larger beings as adults, and in old age lose some mass to become smaller. Dear Theaetetus voices what many of us think about things:
‘Oh yes, indeed, Socrates, I often wonder (thaumazo) like mad what these things can mean; sometimes when I’m looking at them I begin to feel quite giddy’ (155c).
This comment pleases Socrates, who says this ‘wondering’ experience (toȗto to pathos, to thaumazein) is characteristic of a philosopher. He adds that the traditional belief that Iris, the rainbow messenger between humans and gods, was the child of a sea-god called Thaumas, ‘Wonder’ – apparently he represented the wonders of the seas – might have been onto something. Perhaps we can understand this in the sense that it is the unquenchable human curiosity and desire to find out about our environment, which is the conduit for our learning things about the cosmos, and thus becoming, as far as we can, like the gods.
At this point, Socrates shifts to a more authoritative tone. Are there any around who are ‘uninitiated’ (amuētōn)? We might think that this refers to those adults who had been initiated in the Eleusinian and other mystery cults of Greek cities. But Socrates clarifies: he means people who refuse to admit that invisible processes, anything they can’t see or grasp, can exist. They must be pretty tough and difficult people, Theaetetus suggests. They are indeed, Socrates responds, truly uneducated (amousoi, a play on the previous adjective). But the ultimate mystery concerns the fact that everything is really motion (hōs to pan kinesis) and there is really nothing else (156a). A mystery indeed!