Grammar, an affection of a syllable, whereby its measure, or the time wherein it is pronounced, 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; and the economy and arrangement of quantities, that is, the distribution of long and short syllables, makes what we call the number. See Poetry, Part III.

The quantities are used to be distinguished, among grammarians, by the characters \( \sim \), short, as \( \sim \); and \( \sim \), long, as \( \sim \). There is also a common, variable, or dubious quantity; that is, syllables that are at one time taken for short ones, and at another time for long ones; as the first syllable in Atlas, patres, &c.