Is there a ready way to distinguish ἰδέσθαι med or pas?

[ἑκηβόλος]

Is there a ready way to determine when ἰδέσθαι is middle "to see" or passive "to appear"? Is it just left up to an educated (best) guess in context?

[Hylander]

ἰδέσθαι is middle. I'm not sure I've ever seen it to mean "seem" but I could be wrong.

In any event, it's not passive. The aorist passive of ὁράω is ὤφθην, infinitive ὀφθῆναι. The Greek equivalent of "appear" is usually φαίνομαι (passive).

Middle and passive for many verbs are often distinguished by context in the present and perfect systems, but aorist middle and passive have distinct forms.

[ἑκηβόλος]

Is ἰδέσθαι the same verb as the following deponent verb?

1.Lat. videor, to be seen, appear, εἴδεται ἄστρα they are visible, appear Il.
2.c. inf. to appear or seem to be, τοῦτό μοι κάλλιστον εἴδεται εἶναι Od.; also with inf. omitted, τόγε κέρδιον εἴσατο id=Od.; also, εἴσατ᾽ ἴμεν he made a show of going, id=Od.
3.in strictly middle sense, c. dat., ἐείσατο φθογγὴν Πολίτηι she made herself like Polites in voice, Il.:—also to be like, id=Il.

[ἑκηβόλος]

Is principal part εἴδομαι attested outside the 3rd person singular, beside one 1st person singular in Moschus?

[Hylander]

According to LSJ, middle pres. εἴδομαι is used to mean "seem" in epic and lyric, but aor. is εἰσάμην.

http://www.perseus.tufts.edu/hopper/tex ... Dei)%2Fdw1

[RandyGibbons]

Is there a ready way to determine when ἰδέσθαι is middle "to see" or passive "to appear"?

Hi ἑκηβόλος.

If I didn't know better, I could just as easily be persuaded that ἰδέσθαι in this fragment of Xenophanes (DK B32, from scholium BLT on Iliad 11.27) is passive as that it is middle:

ἣν τ’ Ἶριν καλέουσι, νέφος καὶ τοῦτο πέφυκε,
πορφύρεον καὶ φοινίκιον καὶ χλωρὸν ἰδέσθαι.

But the LSJ article Hylander links you to and Hylander himself are definitive: There is no passive ἰδέσθαι.

Is ἰδέσθαι the same verb as εἴδομαι?

No, not in usage, as Hylander again points out. But even as us non-specialists might suspect, etymologically related; see the lemmas εἶδος and ἰδεῖν in Chantraine and εἴδομαι and ἰδεῖν in Beekes.

[Hylander]

ἣν τ’ Ἶριν καλέουσι, νέφος καὶ τοῦτο πέφυκε,
πορφύρεον καὶ φοινίκιον καὶ χλωρὸν ἰδέσθαι.

This is a common idiom, with either active ἰδεῖν or middle ἰδέσθαι. The infinitive supplements an adjective, just like English "to see" or "to behold".

See LSJ *εἴδω :

1. see, perceive, behold, ὀφθαλμοῖσι or ἐν ὀφθαλμοῖσι ἰδέσθαι see before the eyes, Il.1.587, etc.; “ἰδεῖν ἐν ὄμμασιν” E.Or.1020; ἄγε, πειρήσομαι ἠδὲ ἴδωμαι well, I will try and see, Od.6.126, cf. 21.159; mark, observe, Il.4.476, Od.4.412, etc.: folld. by relat. clause, “ἴδωμ᾽ ὅτιν᾽ ἔργα τέτυκται” Il.22.450; “ἀλλ᾽ ἄγε θᾶσσον ἰδώμεθα ὅττι τάδ᾽ ἐστίν” Od.10.44: freq. in inf. after Subst. or Adj., θαῦμα ἰδέσθαι a marvel to behold, Il.5.725; “οἰκτραῖσιν ἰδεῖν” A.Pr.240; “ἐλεινὸς ἰδεῖν” Pl.R.620a.

http://www.perseus.tufts.edu/hopper/tex ... Dei)%2Fdw1

ἰδέσθαι can't be anything but aorist and it simply can't be aorist passive. Aorist passive infinitives always end in -ῆναι.

[RandyGibbons]

You're right, Hylander, (you were clear on this, I wasn't), not even in form can ἰδέσθαι be passive.