Measure
97. From the standpoint of the eye, a measure is that portion of the staff found between two bars, (in certain cases this space may be less than a measure, as e.g., at the beginning and end of a movement); but from the standpoint of the ear a single, isolated measure is not possible, and the term must therefore be defined in the plural form.
Measures are similarly accented groups of evenly-spaced beats, each group having at least one accented and one non-accented beat. The strongest accent falls normally on the first beat in the measure.
Two essential characteristics are involved in the ordinary musical measure:
(1) A group of even beats (or pulses), always felt, though not always actually sounded, one or more of these beats being stronger than the rest;
(2) Certain rhythmic figures (
etc.) which form the
actual musical content of these groups.
The student will note the essential difference between rhythm and measure. Rhythm is the regular recurrence of accent in a series of beats (or pulses), while measure is the grouping of these beats according to some specified system. In listening to a piece of music, two hearers A and B may feel the rhythm equally strongly, but A may subjectively group the beats into—one, two | one, two |—etc., while B feels the groups as—one, two, three, four | one, two, three, four |—etc. Rhythm is thus seen to be a fundamental thing, inherent in the music itself, while measure is to a certain extent at least an arbitrary grouping which musicians have adopted for practical purposes.
98. In syncopation the normal system of accenting is temporarily suspended and the accented tone falls on the regularly unaccented part of the measure. Syncopation may therefore be defined as the temporary interruption of a normal series of accents, i.e., accenting a beat that is usually not accented. Thus e.g., in Fig. 56, measure one has the regular system of accents normally found in four-quarter-measure, (strong accent on one, secondary accent on three); but measure three has only one accent, and it falls on the second beat.
99. Measures are usually classified as simple and compound. A simple measure is one which has but a single accent, i.e., the measure cannot be divided into smaller constituent groups. There are two main classes of simple measures, two-beat measure, and three-beat measure. A compound measure is (as its name implies) one made up by combining two or more simple measures, or by the elaboration of a single measure (in slow tempo) into several constituent groups. The principal compound measures are four-beat and six-beat, both being referred to as compound-duple measures. Five-beat, seven-beat, nine-beat, and twelve-beat measures are also classified as compound measures.
An English writer 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 (
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, (
).
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.
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, two-eighth, and two-half measure, respectively.
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.
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 
are identical in effect with 
.
101. Other varieties of measure sometimes found are 9/8 and 12/8, but
these are practically always taken as three-beat and four-beat measures
respectively, being equivalent to these if each group of three tones is
thought of as a triplet. 
is identical in effect with 
.
102. Quintuple (five-beat) and septuple (seven-beat) measures are occasionally met with, but these are rare and will always be sporadic. The five-beat measure is taken as a combination of three and two, or of two and three (sometimes a mixture of both in the same composition), while theseven-beat measure is taken in groups of four and three, or of three and four.
103. The sign 
is usually understood to mean
four-quarter measure, and the sign 
, two-half measure,
but usage varies somewhat, and the second sign is sometimes used to
indicate four-half measure. It may safely be said however that the sign always indicates
that a half-note has a beat. may occasionally be found indicating four-half measure
but this is rare.
The student will note that the sign is
not a letter C, but an incomplete circle, differentiating
two-beat (imperfect) measure from three-beat (perfect)
measure.
