cwconrad wrote:It would seem to me that there's a difference between the first citation from Jn 21 and the other two from Philemon and James; the first is a matter of a "guesstimate" of a likelihood without any argument to back it up; the other two are assumptions about consequences serving as the basis for action undertaken. I would hesitate to answer the question raised on the basis of these instances; it ought to be possible to ascertain the frequency of usage of οἴεσθαι elsewhere in Hellenistic Koine -- apart, that is, from what we know to be Atticizing, authors.
Yes, οἴεσθαι seems to need a wider context to understand it clearly. I haven't read widely enough to either estimate whether it is being used as a literary allusion or a popular usage. There are a number of references in BDAG to places where it is used (mostly Septuagintal anf early Christian - in keeping with the nature of the work).
Speaking of good Attic authours...For the James passage, consider what Socrates requests for his sons from right near the end of his speech..
Plato, [i]Apology of Socrates[/i], 41e wrote:καὶ οἴονταί τι εἶναι ὄντες οὐδενὸς ἄξιοι
and thinking that they are something when they are really nothing.
It seems to mean that in themselves they think (wrongly suppose) that, as opposed to a outwards show of being something a few phrases earlier ("καὶ ἐὰν δοκῶσί τι εἶναι μηδὲν ὄντες, or if they pretend to be something when they are really nothing," also from 41e). Perhaps something more than just supposing, but like thinking then believing their own conjectures / suppositions - Socrates here seems to be being portrayed as using οἴεσθαι with a negative connotation of some sort.