Mora

Moras, counted as 1-paku, 2-haku, ... using haku (拍) or 1-on, 2-on, ... using on (音), are the rhythmic units of Japanese. A word combines moras to have a function in a phrase, and a morpheme is a combination of moras to have meaning in some context. The Japanese writing system of kana (hiragana & katakana) is based on moras, placing one kana on each mora, with some exceptions with 'softened consonants' like kya, known as yōon.

The difference between moras and syllables is:

A long vowel is counted as 2 moras.

*Aa is one syllable, but two moras, a-a

*Ou is one syllable, but two moras, o-o

*Ei is one syllable, but two moras, e-e

A single n, m, or ng, without a following vowel is counted as one mora, and these three are represented as a single n' mora (haneru oto).

*An is one syllable, but two moras, a-n'

*For example, kankei "relationship" is two syllables, "kan" and "kei", but four moras, ka-n'-ke-e

double consonants are counted as 1 mora. (tsumaru oto). Thus, for example,

*oppai "breasts" is two syllables, "op"-"pai" but four moras, o-(p waiting)-pa-i

*ippai is two syllables, "ip"-"pai" but four moras, i-(p waiting)-pa-i

The Japanese phonetical system doesn't have any consonant teminated moras except n'. They do exist in practice, like the ending -des' for desu, but we consider it to have (neutral or half) vowel of /u/, and t', d' are considered to be /to/, /do/, respectively.

So, for example, 'trumpet' is pronounced torampetto. The moras are to-ra-n'-pe-(waiting t)-to, which makes six, although the original has two syllables, trum-pet.

There are also various reasons to consider Tookyoo "Tokyo" and hanbun "half" both to be two-syllable but four-mora words.

Mora

References