When a short ultima of the nominative is lengthened in an oblique case
a. a proparoxytone becomes paroxytone: θάλαττα θαλάττης, ἄνθρωπος ἀνθρώπου.
b. a properispomenon becomes paroxytone: μοῦσα μούσης, δῶρον δώρον.
c. an oxytone becomes perispomenon in the genitive and dative of the second declension: θεός θεοῦ θεῷ θεῶν θεοῖς.177
When, for a long ultima, a short ultima is substituted in inflection
a. a dissyllabic paroxytone (with penult long by nature) becomes properispomenon: λύ_ω λῦε.
b. a polysyllabic paroxytone (with penult either long or short) becomes proparoxytone: παιδεύω παίδευε, πλέκω πλέκομεν.178
In composition the accent is usually recessive ( cross159) in the case of substantives and adjectives, regularly in the case of verbs: βάσις ἀνάβασις, θεός ἄθεος, λῦε ἀπόλυ_ε.
a. Proper names having the form of a substantive, adjective, or participle, usually change the accent: Ἔλπις (ἐλπίς), Γλαῦκος (γλαυκός), Γέλων (γελῶν).
b. Special cases will be considered under Declension and Inflection.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].