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5.

The vowels i and u serve as consonants when pronounced rapidly before a vowel so as to stand in the same syllable.[1][Compare the English word Indian as pronounced in two syllables or three.] Consonant i has the sound of English consonant y; consonant u (v) that of English consonant w.

Consonant i and u (v) are sometimes called Semivowels.

NOTE 1: The Latin alphabet did not distinguish between the vowel and consonant sounds of i and u, but used each letter (I and V) with a double value. In modern books i and u are often used for the vowel sounds, j and v for the consonant sounds; but in printing in capitals the J and U are avoided: - IVLIVS (Iúlius). The characters J and U are only slight modifications of the characters I and V. The ordinary Englicsh sounds of j and v did not exist in classical Latin, but consonant u perhaps approached English v in the pronunciation of some persons.

NOTE 2: In the combinations qu, gu, and sometimes su, u seems to be the consonant (w). Thus, aqua, anguis, cónsuétus (compare English quart, anguish, suave). In these combinations, however, u is reckoned neither as a vowel nor as a consonant.[2][In such words it is possible that the preceding consonant was labialized and that no distinct and separate consonant u was heard.]