142. The common _school round_ is an example of canon, each voice repeating exactly what the first voice has sung, while this first voice is going on with its melody. The _round_ is therefore defined as a variety of canon in which the imitation is always in unison with the subject.
143. The _fugue_ (Latin, _fuga_ = flight) is a form of contrapuntal composition in which the imitation is always in the dominant key, _i.e._, a fifth above or a fourth below. The imitation (called "the answer") may be an exact repetition of the subject (sometimes called "the question"), but is usually not so.
The _fugue_ differs from the canon also in that the subject is given in complete form before the answer begins, while in the canon the imitation begins while the subject is still going on. The _fugue_ is not nearly so strict in form as the canon and gives the composer much greater opportunity for expressing musical ideas. A canon may be perfect in _form_ and yet be very poor music; this same statement might of course be made about any form, but is especially true in the stricter ones.
TERMS RELATING TO FORMS AND STYLES (_Continued_)
(Sections 144 to 160 relate particularly to terms used in descriptions of _monophonic_ music[33].)
[Footnote 33: There is a very pronounced disagreement among theorists as to what terms are to be used in referring to certain forms and parts of forms and it seems impossible to make a compromise that will satisfy even a reasonable number. In order to make the material in this chapter consistent with itself therefore it has been thought best by the author to follow the terminology of some single recognized work on form, and the general plan of monophonic form here given is therefore that of the volume called _Musical Form_, by Bussler-Cornell.]
144. A _phrase_ is a short musical thought (at least two measures in length) closing with either a complete or an incomplete cadence. The typical _phrase_ is four measures long. The two-measure _phrase_ is often called _section_. The word _phrase_ as used in music terminology corresponds with the same word as used in language study.
145. A _period_ is a little piece of music typically eight measures long, either complete in itself or forming one of the clearly defined divisions of a larger form. The _period_ (when complete in itself) is the smallest monophonic form.