89. The Infinitive and Participle. Infinitives in -ειν and -μεναι follow the general rule: those in -μεν have the same accent as the corresponding forms in -μεναι, as φευγέ-μεν. On the aorist infinitive in -εῖν, see § 85.2.
The forms in -ναι, -σαι accent the penultimate, as ἰέναι, ἁλῶναι, ἐρύσαι. The middle forms of the thematic aorist and perfect are also paroxytone, as πιθέσθαι, λελαθέσθαι, κεκλῆσθαι, τετύχθαι. The ancient grammarians doubted between ἀκάχησθαι, ἀλάλησθαι and ἀκαχῆσθαι, ἀλαλῆσθαι. The former were adopted in the common texts, and were explained as Aeolic forms of the present infinitive (Herodian, ii. 111, 21, ed. Lentz).
It may be conjectured that the forms in -μεναι and -μεν were originally accented on the suffix, like Sanskrit vidmáne, dāvane. If so, this is one of the cases in which the accent of an archaic form in Homer has been lost. Active participles, except the thematic present and future, accent the suffix, as διδούς, στρεφθείς, μεμαώς, λαβών, τεταγών. So the presents ἐών, ἰών.
The participle of the perfect middle is paroxytone. But ἀκαχήμενος follows ἀκάχησθαι.
In composition the infinitive and participle retain the accent of the simple word; in other words, they do not become enclitic. Hence we have imperfect σύν-εχον, but neuter participle συν-έχον.