One is that verbs are generally recessive, meaning that the accent in a verb generally falls as far back as possible. I have noticed that one exception is in certain irregular aorist verbs, such as ἀπῆκα and ξυνῆκα. I’m not aware that there’s any rule for these irregular aorist verbs, although I know that they have the circumflex because they are long vowels on the accented penultimate syllable.
The second rule is that αι and οι, despite being diphthongs and being long for metrical quality, are treated as short for purposes of determining where the accent falls, i.e. the accent can fall on the antepenult instead of the penult. One exception is the optative mood. However, in line 19 of the first book:
ἐκπέρσαι Πριάμοιο πόλιν, εὖ δ’οἴκαδ’ ἱκέσθαι:
there are two infinitives, ἐκπέρσαι, an active infinitive, and ἱκέσθαι, a mediopassive infinitive, where the accent falls on the penult. Is there a reason why this is the case? Is this another exception for the αι and οι rule, like the optative mood, or is this an exception to the verbs being generally recessive rule, like ἀπῆκα and ξυνῆκα?
Bear in mind that infinitives generally are not recessive as they are verbal nouns. The rule applies to finite forms of the verb (Indicative, subjunctive, optative, imperative).
As to ἀπῆκα -ξυνῆκα, I can’t give you an authoritative answer, but I’d hazard that ἧκα is really a contracted form of ἕηκα
ἀπῆκα (Herodotus? in the Homeric texts wouldn’t this be ἀφῆκα?) and ξυνῆκα –
Smyth 426 (emphasis added):
Exceptions to the recessive accent of compound verbs.—a. > The accent cannot precede the augment or reduplication: ἄπειμι am absent, ἀπῆν was absent, εἰσ-ῆλθον they entered, ἀπ-ῆσαν they were absent; ἀφ-ῖκται arrived (cp. ἷκται).
N.—A long vowel or diphthong not changed by the augment receives the accent: ὑπ-εῖκε was yielding (indic. ὑπ-είκω, imper. ὕπ-εικε).
b. The accent cannot precede the last syllable of the preposition before the simple verb nor move back to the first of two prepositions: περίθες put around, συνέκδος give up together (not σύνεκδος), συγκάθες put down together (not σύγκαθες). Compounds of the second aorist active imperatives δός, ἕς, θές, and σχές are thus paroxytone: ἐπίθες set on, περίθες put around, ἐπίσχες hold on.
c. When compounded with a monosyllabic preposition, monosyllabic second aorist middle imperatives in -οῦ from μι-verbs retain the circumflex: προδοῦ betray, ἐνθοῦ put in. But the accent recedes when these imperatives prefix a dissyllabic preposition: ἀπόδου sell, κατάθου put down. The open forms always have recessive accent, as ἔνθεο, κατάθεο.
d. The accent of uncompounded infinitives, participles, aorist passive, perfect passive, and of the second aorist middle imperative (2. p. sing., but see 426 c) is retained in composition.
e. ἀπέσται will be far from, ἐπέσται will be upon do not have recessive accent.
f. Compound subjunctives are differently accentuated in the Mss.: ἀποδῶμαι and ἀπόδωμαι, ἐπιθῆται and ἐπίθηται; the aorist of ἵ_ημι has προῶμαι and πρόωμαι. ἀπέχω has ἀπόσχωμαι. Compound optatives retain the accent of the primitives: ἀποδοῖτο, as δοῖτο. For συνθοῖτο, προσθοῖσθε (746 c) the Mss. occasionally have σύνθοιτο, πρόσθοισθε; and so πρόοιτο.
Bill, thanks for the help with ἀπῆκα /ξυνῆκα. After looking for an instance of ἀπῆκα on the TLG site and not finding any (I did find the other forms used by Herodotus), I think this was a case of forgetting that a smooth stop such as in ἀπ- was preceding a vowel with rough breathing.