32. Elision is dropping or slighting a final short vowel before an initial vowel. The slighted vowel is replaced in writing by an apostrophe (ʼ).
ἀλλʼ ἐγώ for ἀλλὰ ἐγώ
But between the parts of a compound word no apostrophe is written. For consonant changes see § 42.
a. Verse inscriptions show that the ancients did not much care whether they wrote or omitted the elided vowel.
b. Never elided are α and ο in monosyllables, ι in περί, ἄχρι, μέχρι, τί, τι, and ὅτι; also υ. Ὅτʼ must therefore be for ὅτε.
a. Is lost in prepositions and conjunctions.
ἀλλʼ ἐγώ φημι
b. On other words goes back to the penult.
θαυμάστʼ ἔλεξας (θαυμαστά)
a wondrous tale!