In phonology, the subfield of linguistics which concerns speech sounds, morae (singular mora, represented with the Greek letter μ) are the base units of syllable "weight," an abstract property of syllables which can govern several other properties, depending on the language being spoken, such as syllable stress, vowel length and the presence of diphthongs, the tense or lax property of a vowel, the fortis or lenis property of a consonant, consonant geminition, the duration of fricative and nasal consonants, prenasalisation of a syllable, or the tone to be used in a tonal language.

Mora is a Latin word meaning "delay," and its variable usage has led to it having a somewhat nebulous definition. According to the linguist James McCawley, a mora is anything "of which a long (or heavy, or strong) syllable consists of two, and a short (or light, or weak) syllable consists of one." It is possible, however, for syllables to have four or more morae, depending on the language spoken. English, for example, allows up to four morae within a syllable, and such instances (as well as syllables with three morae, and more than four) are called "superheavy" syllables.

Every language handles morae in its own way, forcing this concept to be approached on a language-by-language basis. It is not even strictly phonological in nature, but bleeds into other areas of linguistics. In some languages, such as English, dating back to Old English, morae even have an inherently semantic quality: "content words," those words referring to objects which physically exist and their observable qualities, always have at least two morae.

Because morae determine the cadence and prosody of a language, morae are also relevant to poetic metre, as the macron and breve (or "slash and x," "strong and weak," or "ictus and nonictus") over stressed and unstressed syllables are essentially diacritics to indicate the scansion of monomoraic (single-mora, short or light) and dimoraic (double-mora, long or heavy) syllables.

These scansion diacritics likewise need to be taken in a language-by-language context, as many languages use diacritics to represent morae opposite each other, or in ways that vary by the placement of the mora indicator. Latin uses macrons to show long vowels, but Ancient Greek uses the same symbol to represent a double mora of two short vowels in a row, an acute diacritic to represent high pitch on monomoraic vowels and the second of two short vowels in a double mora, and a circumflex to represent high pitch on the first of two short vowels in a double mora.

Another closely related concept is the chroneme, a unit of vowel or consonant duration which - in some specific languages such as Italian, Latin, Thai, and nearly all Uralic languages - allows minimal pairs to be distinguished from one another, with no other distinguishing feature between the minimally paired words. For example, in Estonian, the words lina ('bed linens,' with a short /n/), linna ('urban,' with a semi-long /n/), and linna ('to the city,' with a long /n/) are only audibly distinguishable from each other by the length of /n/ in each word, yet they do not present any particular difficulty to speakers of Estonian: the distinction is audible to native speakers.

Morae are not to be confused with the Moirae, the Fates of Greek mythology, nor with the Moray eel.

Iron Noder 2019, 22/30

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