I have built a database of Latin words but am having a few problems. I have two databases, one is from Python's CLTK, the other is from online-latin-dictionary.com (OLD). The Python database is derived from Collatinus which is more reliable but there are still problems with it. For example, 'malus' is only conjugated once as an adjective; it does not have the conjugation for 'malus' as a noun meaning apple tree. If it has that mistake you can imagine there are more mistakes like that. Plus the Python CLTK does not have macrons or vowel quantity. The OLD has macrons but there are a ton of mistakes in them. For example, they have 'mālus' marked in the head word with a macron over the 'a' but not in the conjugation. I'm going to go through my database and try to fix this. Sometimes the stem changes quite considerably during conjugation. Here I define 'stem' as that part of the word which is not part of a conjugation ending. I realize I've simply moved the problem of definition over to what is an ending but I hope you get what I mean. I need to know if the vowel quantity ever changes in the stem during conjugation. For example, suppose the quantity of 'a' were long in nominative in 'mālus' but short in the accusative 'malum'. That's just a hypothetical example to show you what I mean. I realize that the accusative of 'mālus' is not 'malum' but 'mālum'.
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According to Asteroids there are 4 nouns that do this: pēs-pĕdis, mās-măris, sāl-sălis, pār-păris.
According to the Greenough Grammar in section 211 he lists the following verbs that have this property.
agō, ēgī , āct-, drive. lavō , lāvī , lōt- (laut-), wash (also regular of first conjugation). capiō , cēpī , capt-, take.
edō , ēdī , ēsum, eat (see § 201). legō ,143 lēgī , lēct-, gather. emō , ēmī , ēmpt-, buy. linō [LI], lēvī ( līvī ), lit-, smear. faciō , fēcī , fact-, make (see § 204). linquō [LIC], -līquī, -lict-, leave. fodiō , fōdī , foss-, dig. nōscō [GNO], nōvī , nōt- ((cō-gnit-, ā-gnit-, ad-gnit-), know. frangō [FRAG], frēgī , frāct-, break.
fugiō , fūgī , ( fugitūrus ), flee. rumpō [RUP], rūpī , rupt-, burst. fundō [FUD], fūdī , fūs-, pour. scabō , scābī , ----, scratch. faciō , iēcī , iact-, throw (-iciō, -iect-). vincō [VIC], vīcī , vict-, conquer.
Is this all of them? I checked with the developer of Collatinus and he said that Collatinus only checks for syllable quantity not vowel quantity. So once I understand how to use that database (I have to learn C++ to do this which will take some time) it will not be possible to get the vowel quantities from that database.
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The Jeanneau dictionary (my favorite Latin dictionary even though it's in French) does have irregular roots listed in its entries. So for the entry of pēs, they do have written pedis, with the hat over the e. (sorry I haven't yet figured out how to write the hat yet). And for the entry of vinco, they do have vīncī, written down. So I guess I can get the vowel quantity changes that way.
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Here's another relevant passage from the Greenough Grammar
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, ort: 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 . Sodē-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 .