Omission of the Augment.—a. In Attic tragedy the augment is sometimes omitted in choral passages, rarely in the dialogue parts (messengers' speeches), which are nearer akin to prose.
b. In χρῆν (from χρὴ ἦν) the augment is strictly unnecessary, but is often added (ἐχρῆν) since the composition of χρῆν was forgotten.
c. In Homer and the lyric poets either the syllabic or the temporal augment is often absent; as φάτο and ἔφατο, βῆν and ἔβην, ἔχον and εἶχον. Iteratives ( cross495) in Hom. usually have no augment (ἔχεσκον).
N.—In Homer the absence of the augment represents the usage of the parent language, in which the augment was not necessarily added to mark past time. It is therefore erroneous, historically, to speak of the omission of the augment in Homer.
d. In Herodotus the syllabic augment is omitted only in the case of pluperfects and iteratives in σκον; the temporal augment is generally preserved, but it is always omitted in verbs beginning with αι, αυ, ει, ευ, οι, and in ἀγι_νέω, ἀεθλέω, ἀνώγω, ἔρδω, ἐάω, ὁρμέω, etc.; in others it is omitted only in some forms (as ἀγορεύω, ἄγω, ἕλκω, ὁρμάω), and in others it is variable (ἀγγέλλω, ἅπτω, ἄρχω, ἐπίσταμαι, ἀνέχομαι); in cases of Attic reduplication the augment is never added. Hdt. omits the augment for the reduplication in the above verbs.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].