An English writer[23] classifies measures as duple, triple, or quadruple, specifying that a simple measure is one in which each beat is represented by a note whose value can be divided into halves ([Illustration] etc.) and that a compound measure is one in which each beat is represented by a dotted-note, whose value can be divided into three parts, ([Illustration]). There is thus seen to be considerable difference of opinion as to the meaning of the words _simple_ and _compound_ when applied in this connection, the principal question at issue being whether four-beat measure is an individual variety, or whether it is a variety compounded out of two-beat measures, either by placing two of these in a group or by the elaboration of a single measure into a larger number of beats, as is often necessary in slow tempi. Perhaps the easiest way out of the difficulty is to admit that both may be true--but in different compositions. That is, it is frequently impossible to tell whether a composition that is being listened to is in two-beat, or in four-beat measure; and yet it _is_ sometimes possible so to discriminate. Since, however, one cannot in the majority of cases distinguish between two-beat and four-beat measures, it will probably be best to leave the original classification intact and regard four-beat measure as a compound variety.
[Footnote 23: Pearse--Rudiments of Musical Knowledge, p. 37.]
100. The _commonest varieties of measure_ are:
1. _Duple_ (sometimes called even measure, or even time), in which there are two beats, the first one being accented. Examples of duple measure are 2/4, 2/8, 2/2, two-quarter,[24] two-eighth, and two-half measure, respectively.
[Footnote 24: For explanation of terminology, see p. 48, Sec. 106.]
2. _Triple_, (the old perfect measure), in which there are three beats, the first one being accented, the second and third unaccented. Examples are 3/8, 3/4, 3/2, three-eighth, three-quarter, and three-half measure, respectively.
3. _Quadruple_, in which there are four beats, the first and third being accented (primary accent on _one_, secondary accent on _three_), the second and fourth unaccented. (See note above, under Sec. 99.)
4. _Sextuple_, in which there are six beats, the first and fourth being accented, the others not. In rapid tempi this is always taken as compound duple measure, a dotted quarter note having a beat. It will be noted that the two measures [Illustration] are identical in effect with [Illustration].