Reduplication is the doubling of the sound standing at the beginning of a word. It is used in the perfect, pluperfect, and future perfect tenses in all the moods, to denote completed action. It is sometimes found also in the present and second aorist.439D
Reduplication (or the augment for the reduplication) is generally retained in Hom. Exceptions are ἔρχαται and ἔρχατο from ἔργω
Verbs beginning with a simple consonant (except ρ) or with a stop and a liquid (λ, μ, ν, ρ) place the initial consonant with ε before the stem. λύ_ω
a. Exceptions: verbs beginning with γν, most of those with γλ, and some with βλ. Thus, γνωρίζω
An initial aspirate is reduplicated by the corresponding smooth stop: φονεύω
In all other cases the reduplication is formed like the augment.
a. Verbs beginning with a short vowel lengthen the vowel, as ἄγω
b. Verbs beginning with two or more consonants (except a stop with a liquid), a double consonant, and ρ simply prefix ε. ρ is here doubled (cp. cross429 a).
Hom. has ῥε-ρυπωμένος (ῥυπόω
The verbs mentioned in 431 which originally began with a consonant now lost, reduplicate regularly. Since the reduplicated consonant has disappeared only ε is left, and this often contracts with the initial vowel of the theme. Thus, ἔα_γα for ϝε-ϝα_γα from ϝάγνυ_μι
Pluperfect.—The pluperfect prefixes the syllabic augment ε to the reduplicated perfect beginning with a consonant; when the perfect stem begins with a vowel the pluperfect retains the prefix of the perfect.
Thus perf. λέλυκα, λέλυμαι, plup. ἐ-λελύκη, ἐ-λελύμην; perf. ἔ-σταλκα, ἔ-σταλμαι, plup. ἐ-στάλκη, ἐ-στάλμην from στέλλω
a. Verbs showing ‘Attic’ reduplication ( cross446), in almost all cases augment the pluperfect.
b. The verbs of 431 follow the perfects of 443; as ἐά_γη (ἄγνυ_μι), ἐώσμην (ὠθέω), εἵμην (ἵ_ημι), ἐρρώγη from (ϝ) ρήγνυ_μι. ἵστημι forms εἱστήκη ( = ἐ- (ς) εστηκη), Ion. and poet. ἑστήκη (rare in Att. prose). ἔοικα
Hdt. has οἶκα (for ἔοικα), ἔωθα, ἐώθεα; Hom. has ἔωθεν and εἴωθε.445
Some verbs beginning with a liquid or μ take ει instead of the reduplication: λαμβάνω (λαβ-)
a. εἴληφα is from σε-σληφα by 37 (cp. Hom. ἔλλαβον for ἐ-σλαβον), εἵμαρται is from σε-σμαρται (cp. Hom. ἔμμορε). The other forms are probably analogues of εἴληφα.446
Attic Reduplication.—Some verbs whose themes begin with α, ε, or ο, followed by a single consonant, reduplicate by repeating the initial vowel and the consonant and by lengthening α and ε to η, ο to ω. Thus ἀγείρω
a. The name ‘Attic’ was given by the Greek grammarians to this form of reduplication though it occurs in Homer and in the other dialects.
—In Hom. ‘Attic’ reduplication is even more frequent than in Attic; thus, ἐδηδώς from ἔδω
Reduplication in the Present.—A few verbs reduplicate in the present by prefixing the initial consonant and ι, as γί-γνομαι, γι-γνώσκω, μι-μνῄσκω, τί-κτω for τι-τ (ε) κω, πί_-πτω for πι-π (ε) τω, ἵ-στημι for σι-στημι, τί-θημι for θι-θημι ( cross125 a), δί-δωμι. πίμ-πλη-μι
a. In some verbs the reduplication belongs to the verbal stem: βιβάζω
Reduplication in the Second Aorist.—ἄγω
Hom. has many reduplicated second aorists, as πέ-πιθον from πείθω (πιθ-)
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].