Plato in general uses 'episteme' more often, because he examines, tries to understand and define, certain areas of knowledge.
For oide, remember also a previous post in this thread where I mentioned the word "eidenai". Out of this alternative for knowledge come also the words eidos (appearance, form, species), idea, syneidesis (consciousness). Eidenai is more akin to seeing and vision, epistasthai is more akin with command over knowledge and gignoskein is more akin with nous (intellect and mainly the higher functions of it), and although all can be used as synonyms to a certain degree, there seem to keep these nuances, with gignoskein being the more general and inclusive of all.
This is of course a schematical approach, I hope not betraying very much the reality. There are more! Phronesis (wherefrom sophrosene, which is not just temperance) is related with phren (mind). Plotinos writes that "sophia (wisdom) and phronesis (sapience) come from the theoria (theory, vision, contemplation) of nous (intellect), and nous comes from epaphe (touching)... Phronesis goes around being, nous goes beyond being (Enneades 1, 2, 6 and 1, 3, 5), therefore there is some higher contact/touching of the nous with a reality that transcends even being, out of which all sorts of our knowledge spring according to the quality of that contact.
You may have no idea how helpful (and humbling) these exchanges are.
1. Apparently, then, there are three etymological groupings - centered on εἰδέναι, ἐπίστασθαι, and γιγνώσκειν. (Have I got those spelled correctly? Are they verbs or nouns? As you see, I've finally learned to type the Greek.) You say that all the words can be used pretty much interchangeably to refer to knowlege; but we also may, if we wish, play up their slightly differing connotations. Then, as you say, there are more words if we broaden our scope to consider other mental activities in addition to knowledge.
2. Thank you for mentioning 'φρόνησις' and for clarifying that that is where we get 'σωφροσύνη', which is not just temperance. That raises for me two additional questions about the Charmides text.
(a) As we have been discussing, Critias at 165b asserts that temperance is self-knowledge (γνῶσις), and he subsequently agrees at 165b-c to Socrates' suggestions that it is a science (ἐπιστήμη) and the science of one's self. I'm clear now, thanks to your advice, that there's no reason to suppose Greeks of Plato's day would have seen any logical problems with the word-shift. But now let's go on. Up until this point, Socrates and Critias have been talking just about temperance (σωφροσύνη). But at 165e, Socrates says that it is "temperance or wisdom" that is to be identified with this science of one's self. And immediately following, also at 165e, Critias ceases mentioning 'temperance' at all and says instead simply - referring to the science under discussion - that "wisdom is not like the other sciences." Then, in their subsequent discussion (which is quite lengthy), Socrates and Critias mainly say it is wisdom they are talking about, though they sometimes drop back to locutions like "wisdom or temperance". So here is my question: What is the word for "wisdom" that Socrates and Critias are using in this conversation - 'σοφία' or 'φρόνησις'? Would Socrates' and Critias' "wisdom or temperance" locution be more equivocal if they used 'σοφία', and less (because of the link with 'σωφροσύνη') if they used 'φρόνησις'?
(b) Earlier in the dialogue (161b), Charmides suggests that temperance is "doing one's own business". (I believe this suggestion is obviously flawed, though Socrates never refutes the hypothesis in this dialogue.) Strikingly, Socrates in the Republic (Book IV, 433b) claims that "doing one's own business" is the definition of justice. Am I right in speculating that temperance (σωφροσύνη) and justice (δικαιοσύνη) are etymologically related, both having something to do with '-συνε'? What does '-συνε' mean? Can you, off-hand, think of any other '-συνε' words?
3. Plotinus' comments no doubt may shed some light on interpretations of subsequent Christian texts, a subject evidently of much interest to you and others on this board. I don't regard him a reliable authority on Plato's Greek usage. He lived five hundred years after Plato, in a different society, and championed a very different metaphysical position.
They use the word episteme. Sophia would not be that approrpriate, since it is closer to a higher knowledge. The translation of the whole passage should use the word science to be more accurate.
Don't bother about σύνη, it is the ending of the word, not the root. And between *dik and *fro there seems to be not immediate relation. The "so" of sophrosene is a word of its own, meaning "save", "intact", "healthy", thus adding to phrosene (never occuring alone, contrary to the similar phronesis. Phronesis as Sophrosyne is always written with that "so") a nuance of having or keeping safe, healthy, your phronesis. The root is to be found at the *fro of fronesis and -frosene).
I understand your reservation about Plotinus; just had it more convenient, and this in particular excerpt reflects the point of our discussion. See Plato's Timaeus 90a : God gave the sovereign part of the human soul to be the divinity of each one, being that part which, as we say, dwells at the top of the body, inasmuch as we are a plant not of an earthly but of a heavenly growth, raises us from earth to our kindred who are in heaven. And in this we say truly; for the divine power suspended the head and root of us from that place where the generation of the soul first began, and thus made the whole body upright.
Just after that Plato even uses the word aphe (touch) to describe the divine reception of knowledge by nous or grasping of the nous by god.
"They use the word episteme. Sophia would not be that approrpriate, since it is closer to a higher knowledge. The translation of the whole passage should use the word science to be more accurate."
I'm not sure we're on the same wave-length. You seen here to be responding to my earlier question as to what word they use in the Charmides for "science". But my (2a) of Aug 9 asked what words they use for "temperance" and "wisdom". To confirm, please help me out with a further fill-in-the-brackets exercise (all from Jowett's translation).
166e. Critias. "Wisdom () alone is a science of other sciences and of itself."
167a. Socrates. "Then the wise () or temperate () man, and he only, will know himself, and be able to examine what he knows or does not know . . ."
169a. Socrates. "If there be such a class [of self-related things], that science which is called wisdom () or temperance () is included."
These questions relate to an interpretive analysis of the Charmides that I've been developing - namely, that Socrates and Critias seem in the second half of the dialogue to cease genuinely seeking a definition of temperance, and seem instead to be asking about wisdom or perhaps about some equivocal thing that they call 'temperance or wisdom'.