The _measure_ is a group of beats,--two, three, four, or more, at the option of the composer.

The bounds of the measures are visibly represented (on the written or printed page) by vertical lines, called bars; and are rendered orally recognizable (to the hearer who does not see the page) by a more or less delicate emphasis, imparted--by some means or other--to the _first_ pulse or beat of each measure, as accent, simply to mark where each new group begins.

Those who play or sing can imagine how vague, and even chaotic, a page of music would look if these vertical bars were omitted; and how much more difficult it would be to read than when these (not only accustomed, but truly necessary) landmarks are present.

Precisely the same unintelligible impression must be, and is, conveyed to the hearer when _his_ landmarks, the accents, are not indicated with sufficient emphasis or clearness to render him sensible of the beginning of each new measure.
* * * * * * The same primary system of measurement and association which is employed in enlarging the beats to measures, is then applied to the association of the measures themselves in the next larger units of musical structure, the Motive, Phrase, Period, and so forth.

Unlike the measures, which are defined by the accents at their _beginning_, these larger factors of form are defined chiefly at their _end_, by the impression of occasional periodic interruption, exactly analogous to the pauses at the end of poetic lines, or at the commas, semicolons and the like, in a prose paragraph.