The so-called three-mora rule is a linguistic rule which argues that an enclitic cannot be more than three moras in length. That is, three shorts, a long and a short, or a short and a long. Within a single word the most that can follow the accent is a long and a short.
With few exceptions, Latin words are stressed on the penult (second-to-last syllable) if it is "heavy" (having a long vowel or diphthong or ending in a consonant), and on the antepenult (third-to-last syllable) if the penult is "light" (ending with a short vowel.)
- Condĭtum "founded" = co•n—di—tum (heavy, light, final) = cónditum
- Condītum "seasoned" = co•n—di•i—tum (heavy, heavy, final) = condítum
- Conductum "brought together" = co•n—du•c—tum (heavy, heavy, final) =condúctum
( - marks a syllable boundary, • marks a mora boundary)
Moraic analysis of Latin
If one counts all "light" syllables as one mora and all "heavy" syllables as two morae, it becomes clear that the accent is essentially always placed three morae before the end of the word. Note, however, that for this analysis to work, one must always count the final syllable as one mora, regardless of its actual syllabic composition.
- In condĭtum the third mora from the end is the n of the first syllable, so the accent falls on cón-
- In condītum the third mora from the end is the first part of the ī in the second syllable, so the accent falls on dí-
- In conductum the third mora from the end is the du of the second syllable, so the accent falls on duc-
|5th mora||4th mora||3rd mora||2nd mora||final||accent|
A somewhat different, and possibly more accurate, analysis is to consider the final syllable as extra metric; then the accent always falls on the syllable with the penult metric mora, and there is no need to define a special type of mora counting for the last syllable.
Many other languages have similar but not identical rules for the placement of the accent:
- Arabic dialects (and certain other Semitic languages) originally used a similar rule, but this has been complicated by the loss of most final vowels.
- Sanskrit (and certain other Indo-Aryan languages) use a version of this rule that allowed for placement on the fourth-to-last syllable if the antepenult was light.
- Ancient Greek had a totally different rule, but it likewise restricted the accent to the last three syllables and could be seen as mora-based.
- Godfrey of Fontaine's Abridgement of Boethius of Dacia's: Modi ... -Boethius (of Dacia), Godfrey (of Fontaines), A. Charlene Senape Mac Dermott - 1980 Page 112 "It's impossible to throw it back to the preceding word [as a real enclitic does] because of the three-mora rule. An enclitic cannot be more than three-moras in length, i.e. three shorts, a long and a short, or a short and along. Within a single word the most that can follow the accent is a long and a short."
- James W. Marchand The Sounds and Phonemes of Wulfila's Gothic -1973 Page 96 "5.31 The “Dreimorengesetz” The prevailing theory accounting for developments of inflectional endings from IE to Germanic to "the various Germanic languages is the theory of Dreimorigkeit .. This theory, as it is set down by its outstanding exponent, Hermann Hirt, is as follows :“7 Es gab im Idg. zweimorige und ..."..."
- Selected Writings: Phonological studies. I - Page 263 Roman Jakobson - 2002 "The "limitational rule" of Greek accentuation is actually more precise than the three-syllable rule and more exhaustive than the three-mora rule which proved unable to embrace all the possible cases: the vocalic morae between the accented .."