Grammar, is an affection of a syllable, by which its measure, or the time it occupies in pronunciation, is ascertained; or that which determines the syllable to be long or short.

Quantity is also the object of prosody, and distinguishes verse from prose; whilst the economy and arrangement of quantities, that is, the distribution of long and short syllables, constitutes what is called number.

Quantities are usually distinguished amongst grammarians by the characters of short and long. There is also a common, variable, or dubious quantity; that is, syllables which are at one time taken for short, and at another time for long ones.