To this general rule there are exceptions.
a. Enclitics.—All the forms of φημί
b. Imperatives.—(1) The second person sing. of the second aorist active imperative of five verbs is oxytone: εἰπέ
(2) The second aorist middle (2 sing.) is perispomenon, as λαβοῦ, παραβαλοῦ, καθελοῦ.
c. Contracted verbs are only apparent exceptions: thus, e.g., τι_μᾷ for τι_μάει, δηλοῦσι for δηλόουσι, φιλεῖν for φιλέειν. So the subjunctive of the first and second aorist passive λυθῶ for λυθέω, φανῶ for φανέω; the optatives λυθεῖμεν from λυθέ-ι_-μεν, διδοῖμεν from διδό-ι_-μεν; the futures φανῶ for φανέω, φανοῖμι for φανέοιμι, φανεῖν for φανέειν, φανῶν for φανέων; λιπεῖν for λιπέεν; and the present and second aorist active and middle subjunctive of most μι-verbs, as τιθῶ for τιθέω, ἱστῶμαι, θῶμαι, perf. κεκτῶμαι. On διδοῦσι, τιθεῖσι, see cross463 d.
N. 1.—In athematic optatives the accent does not recede beyond the diphthong containing -ι_-, the sign of the optative mood: ἱσταῖο, ἱσταῖμεν, ἱσταῖτο, διδοῖτο; and so in λυθεῖμεν, λυθεῖεν.
d. Poetic forms sometimes fail to follow the rule, as ἐών
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].