Morae

A mora (plural morae or moras; often symbolized μ) is a unit in phonology that determines syllable weight, which in some languages determines stress or timing. The definition of a mora varies. In 1968, American linguist James D. McCawley defined it as "something of which a long syllable consists of two and a short syllable consists of one". The term comes from the Latin word for "linger, delay", which was also used to translate the Greek word chronos (time) in its metrical sense.

Monomoraic syllables have one mora, bimoraic syllables have two, and trimoraic syllables have three, although this last type is relatively rare.

In general, morae are formed as follows:

In general, monomoraic syllables are called "light syllables", bimoraic syllables are called "heavy syllables", and trimoraic syllables (in languages that have them) are called "superheavy syllables". Some languages, such as Old English and present-day English, can have syllables with up to 4 morae.

A prosodic stress system in which moraically heavy syllables are assigned stress is said to have the property of quantity sensitivity.

For the purpose of determining accent in Ancient Greek, short vowels have one mora, and long vowels and diphthongs have two morae. Thus long ē (eta: η) can be understood as a sequence of two short vowels: ee.

Ancient Greek pitch accent is placed on only one mora in a word. An acute (έ, ή) represents high pitch on the only mora of a short vowel or the last mora of a long vowel (é, eé). A circumflex (ῆ) represents high pitch on the first mora of a long vowel (ée).

In Old English, short diphthongs and monophthongs were monomoraic, long diphthongs and monophthongs were bimoraic, consonants ending a syllable were each a mora, and geminate consonants added a mora to the preceding syllable. In Modern English, the rules are similar, except that all diphthongs are bimoraic. In English, and likely also in Old English, syllables cannot have more than 4 morae, with loss of sounds occurring if a syllable would have more than 4 otherwise. From the Old English period through to today, all content words must be at least 2 morae long.

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