§606. Derivatives

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, ort: as, amĕm, amĕr, dīcerĕr, amĕt (compare amēmus), dīcerĕt, audĭt,fĭt.
• A few long stem-syllables are shortened: as,ācer, ăcerbus. Sodē-iĕrō andpē-iĕrō, weakened from iūrō.

b. Forms from the same root often show inherited variations of vowel quantity (see § 17): as, dīcō (cf. maledĭcus); dūcō (dŭx, dŭcis); fīdō ( perfĭdus) vōx, vōcis ( vŏcō); lēx, lēgis ( lĕgō).

c. Compounds retain the quantity of the words which compose them as, oc-cĭdō ( cădō), oc-cīdō ( caedō), in-īquus ( aequus).