Qualitative Vowel Gradation.—In the same root or suffix we find an interchange among different vowels (and diphthongs) similar to the interchange in sing, sang, sung.
a. This variation appears in strong grades and in a weak grade (including actual expulsion of a vowel—in diphthongs, of the first vowel). Thus, φέρ-ω I carry, φόρ-ο-ς tribute, φώρ thief, φαρ-έ-τρᾱ quiver, δί-φ ρ-ο-ς chariot (twocarrier), λείπ-ω I leave, λέ-λοιπ-α I have left, λιπ-εῖν to leave. The interchange is quantitative in φόρ-ο-ς φώρ (cp. 27).
b. When, by the expulsion of a vowel in the weak grade, an unpronounceable combination of consonants resulted, a vowel sound was developed to render pronunciation possible. Thus, ρα or αρ was developed from ρ between consonants, as in πα-τρά-σι from ṛατρ-σι (262); and α from ν, as in αὐτό-μα-το-ν for αὐτο-μṇ-τον automaton (acting of its own will), cp. μέν-ο-ς rage, μέ-μον-α I yearn. So in ὀνομαίνω name for ὀνομṇ-ι̯ω; cp. ὄνομα.
c. A vowel may also take the place of an original liquid or nasal after a consonant; as ἔλῡσα for ἐλῡσṃ. This ρ, λ, μ, ν in b and c is called sonant liquid or sonant nasal.