[*] 606. Rules for the Quantity of Derivatives are:— [*] a. Forms from the same stem have the same quantity: as, ămō , ămāvistī; gĕnus, gĕneris. Exceptions.—
- bōs , lār,mās, pār , pēs , sāl,—alsoarbōs,—have a long vowel in the nominative, though the stem-vowel is short (cf. genitive bŏvis etc.).
- Nouns in -or, genitive -ōris, have the vowel shortened before the final r: as,honŏr. (But this shortening is comparatively late, so that in early Latin these nominatives are often found long.)
- Verb-forms with vowel originally long regularly shorten
it before final m, r,
[*] Note.--The final syllable in t of the perfect was long in old Latin, but is short in the classic period.
- A few long stem-syllables are shortened: as,ācer, ăcerbus . Sodē-iĕrō andpē-iĕrō, weakened from iūrō .
[*] Note.--Greek words compounded with πρό have o short: as, prŏphēta , prŏlŏgus . Some Latin compounds of prō have o short: as, prŏficīscor , prŏfiteor . Compounds with ne vary: as, nĕfās , nĕgō , nĕqueō , nēquam .