The stem of the perfect and pluperfect middle and passive is the reduplicated verb-stem, to which the personal endings are directly attached. λέλυ-μαι
A thematic vowel precedes the ending in Hom. μέμβλεται (μέλω
The stem of the perfect middle is in general the same as that of the first perfect active as regards its vowel ( cross557), the retention or expulsion of ν ( cross559 a), and metathesis ( cross559 d).
The vowel of the perfect middle stem should show the weak form when there is variation between ε (ει, ευ): ο (οι, ου): α (ι, υ). The weak form in α appears regularly in verbs containing a liquid ( cross479): that in υ, in πέπυσμαι from πυνθάνομαι (πυθ-, πευθ-)
The vowel of the present has often displaced the weak form, as in πέπλεγμαι (πλέκ-ω
ν is retained in endings not beginning with μ, as φαίνω (φαν-)
Future Perfect.—The stem of the future perfect is formed by adding -σόε- to the stem of the perfect middle. A vowel immediately preceding -σόε- is always long, though it may have been short in the perfect middle.
Hom. has δεδέξουαι, μεμνήσομαι, κεκλήσῃ, κεχολώσεται; κεκαδήσομαι, πεφιδήσεται are from reduplicated aorists.581
Not all verbs can form a future perfect; and few forms of this tense occur outside of the indicative: διαπεπολεμησόμενον Thuc. 7. 25 is the only sure example of the participle in classical Greek. The infinitive μεμνήσεσθαι occurs in Hom. and Attic prose.583
The periphrastic construction ( cross601) of the perfect middle (passive) participle with ἔσομαι may be used for the future perfect, as ἐψευσμένος ἔσομαι
Future Perfect Active.—The future perfect active of most verbs is formed periphrastically ( cross600). Two perfects with a present meaning, ἕστηκα
Hom. has κεχαρήσω and κεχαρήσομαι from χαίρω (χαρ-)
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].