a) In Plurals; as, portīs, hortīs, nōbīs, vōbīs, nūbīs (Acc.).
b) In the Second Person Singular Perfect Subjunctive Active; as, amāverīs, monuerīs, audīverīs, etc. Yet occasional exceptions occur.
c) In the Second Person Singular Present Indicative Active of the Fourth Conjugation; as, audīs.
d) In vīs, force; īs, thou goest; fīs; sīs; velīs; nōlīs; vīs, thou wilt (māvīs, quamvīs, quīvīs, etc.).
6. Final -us is usually short, but is long:—
a) In the Genitive Singular and in the Nominative, Accusative, and Vocative Plural of the Fourth Declension; as, frūctūs.
b) In the Nominative and Vocative Singular of those nouns of the Third Declension in which the u belongs to the stem; as, palūs (-ūdis), servitūs (-ūtis), tellūs (-ūris).
[365]. Greek Nouns retain in Latin their original quantity; as, Aenēā, epitomē, Dēlos, Pallas, Simoīs, Salamīs, Dīdūs, Paridī, āēr, aethēr, crātēr, hērōăs. Yet Greek nouns in -ωρ (-ōr) regularly shorten the vowel of the final syllable; as, rhētŏr, Hectŏr.
VERSE-STRUCTURE.
GENERAL PRINCIPLES.
[366]. 1. The metrical unit in versification is a short syllable, technically called a mora (
). A long syllable (
