Herbert Weir Smyth, A Greek Grammar for Colleges

DATIVE DUAL AND PLURAL

Ἄραψ (Ἀραβ-) Ἄραψι, μάστι^ξ (μαστι_γ-) μάστιξι, φύλαξ (φυλακ-) φύλαξι, σῶμα (σωματ-) σώμασι (98), ἐλπίς (ἐλπιδ-) ἐλπίσι (98), ὄρνι_ς (ὀρνι_θ-) ὄρνι_σι (98), ἐλέφα_ς (ἐλεφαντ-) ἐλέφα_σι, θήρ (θηρ-) θηρσί.

a. Stems in ντ drop ντ and lengthen the preceding vowel (100): λέων (λεοντ-) λέουσι, γίγα_ς (γιγαντ-) γίγα_σι.

b. Stems in ν drop ν without lengthening the preceding vowel (if short): δαίμων (δαιμον-) δαίμοσι, ποιμήν (ποιμεν-) ποιμέσι, φρήν mind (φρεν-) φρεσί.

N.—Strictly ν is not dropped, but since the stem of the dat. pl. is weak in form (253 a) the ν stood originally between two consonants and should become α (35 b). Thus, φρασί in Pindar is for φρṇσι. Attic φρεσί borrows its ε from φρένες, φρενῶν, etc. So ποιμέσι, for ποιμασι from ποιμṇσι, because of ποιμένες, etc.

c. ρς is not changed to ρρ (79 a).

[*] 250 D. 1. Hom. has only -οιιν in the gen. and dat. dual.

2. In the dat. pl. Hom. has -σι (βέλεσ-σι, δέπασ-σι), and in a few cases -εσι, reduced from -εσσι (ἀνάκτ-εσι); -σσι occurs after vowels (γένυ-σσι; for γένυ_σι?). -εσσι was added both to stems not ending in ς (πόδ-εσσι, βό-εσσι, ἄνδρ-εσσι, ὀΐ-εσσι, 274 D.), and even to stems in ς (έπέ-εσσι). Hom. has also ποσσί, ποσί; Pind. χαρίτεσσι, θέμισσι. Tragedy has this -εσσι (κορύθ-εσσι), and so Aeolic, and the Doric of Corinth.