Exultat telis, et luce coruscus aëna.”
Additam supra vidimus h litteram, et ahena factum. Sic in illo quoque Vergilii versu in optimis libris scriptum invenimus:
“Aut foliis undam tepidi dispumat aheni.”
I consonant has the sound of i in the English word onion.
The grammarians all express themselves in nearly the same terms as to its character:
[Serg. Explan. in Art. Donat. Keil. v. IV. p. 520.] I et u varias habent potestates: nam sunt aliquando vocales, aliquando consonantes, aliquando mediae, aliquando nihil, aliquando digammae, aliquando duplices. Vocales sunt quando aut singulae positae syllabam faciunt aut aliis consonantibus sociantur, ut Iris et unus et Isis et urna. Consonantes autem sunt, cum aliis vocalibus in una syllaba praeponuntur, aut cum ipsae inter se in una syllaba conjunguntur. Nisi enim et prior sit et in una syllaba secum habeat conjunctam vocalem, non erit consonans i vel u. Nam Iulius et Iarbas cum dicis, i consonans non est, licet praecedat, quia in una syllaba secum non habet conjunctam vocalem, sed in altera consequentem.
The grammarians speak of i consonant as different in sound and effect from the vowel i; and, as they do not say how it differs, we naturally infer the variation to be that which follows in the nature of things from its position and office, as in the kindred Romance languages.
Priscian says:
[Keil. v. II. p. 13.] Sic i et u, quamvis unum nomen et unam habeant figuram tam vocales quam consonantes, tamen, quia diversum sonum et diversam vim habent in metris et in pronuntiatione syllabarum, non sunt in eisdem meo judicio elementis accipiendae, quamvis et Censorino, doctissimo artis grammaticae, idem placuit.
It would seem to be by reason of this twofold nature (vowel and consonant) that i has its ‘lengthening’ power. Probus explains the matter thus: