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Allen and Greenough/ New Latin Grammar

QUANTITY/ Derivatives

606. Rules for the Quantity of Derivatives are:—

a. Forms from the same stem have the same quantity: as, ămō, ămāvistī; gĕnus, gĕneris.

Exceptions.

  1. bōs, lār, mās, pār, pēs, sāl,—also arbōs,—have a long vowel in the nominative, though the stem-vowel is short (cf. genitive bŏvis etc.).
  2. 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.)
  3. Verb-forms with vowel originally long regularly shorten it before final m, r, or t: as, amĕm, amĕr, dīcerĕr, amĕt (compare amēmus), dīcerĕt, audĭt, fĭt.

    Note— The final syllable in t of the perfect was long in old Latin, but is short in the classic period.

  4. A few long stem-syllables are shortened: as, ācer, ăcerbus. So dē-iĕrō and pē-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).

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.

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