I, i, the ninth letter of the Latin alphabet, a vowel; for even the old grammarians distinguished it from the consonant written with the same character; see the letter J. The short i is, next to e, the least emphatic of the Latin vowels, and serves, corresp. to the Gr. o, as a connecting sound in forming compounds: aerifodina, aeripes, altitudo, altisonus, arcitenens, homicida, etc. It is often inserted in Latin words derived from Greek: mina, techina, cucinus, lucinus (for mna, techna, cycnus, lychnus, etc.); cf. Ritschl, Rhein. Mus. 8, p. 475 sq.; 9, p. 480; 10, p. 447 sq. And in similar manner inserted in arguiturus, abnuiturus, etc. The vowel i is most closely related to u, and hence the transition of the latter into the former took place not only by assimilation into a following i, as similis, together with simul and simultas; facilis, together with facul and facultas; familia, together with famul and famulus; but also simply for greater ease of utterance; so that, from the class. per. onward, we find i written in the place of the older u: optimus, maximus, finitimus, satira, lacrima, libet, libido, etc., instead of the earlier optumus, maxumus, finitumus, satura, lacruma, lubet, lubido, etc.; cf. also the archaic genitives cererus, venerus, honorus, nominus, etc., for the later Cereris, Veneris, honoris, nominis, etc., the archaic orthography caputalis for capitalis, etc. For the relation of i to a and e, see those letters. Examples of commutation between i and o are rare: -agnitus, cognitus, together with notus, ilico from in loco, the archaic forms ollus, ollic for ille, illic, and inversely, sispes and sispita for sospes and sospita. As an abbreviation, I (as the sign of the vowel i) denotes in, infra, ipse, Isis, etc.: IDQ iidemque, I. H. F. C. ipsius heres faciendum curavit, IM. immunis, IMP. imperium, imperator, etc. The capital letter I is often confounded with the numeral I. (unus, primus).