Both vocal and instrumental music have been written in contrapuntal style. The familiar two- and three-part "inventions" by Bach are excellent examples of instrumental counterpoint, while such choruses as those in "The Messiah" by Handel illustrate the highest type of vocal counterpoint.
140. Imitation is the repetition by one part, of a subject or theme previously introduced by another part. If the imitation is exact, the term strict imitation is applied, but if only approximate, then the term free imitation is used in referring to it. The repetition need not have the exact pitches of the subject in order to be strict; on the contrary the imitation is usually at the interval of an octave, or a fifth, or a second, etc. Fig. 57 shows an example of strict imitation in which the third part comes in an octave lower than the first part.
141. A canon is a contrapuntal composition in the style of strict imitation, one part repeating exactly (but at any interval) what another part has played or sung. The term "canonic style" is sometimes applied to music in which the imitation is not exact. An example of three-part canon is given in Fig. 57.
CANON IN THREE VOICES, IN THE UNISON AND OCTAVE
The word canon means law, and was applied to this particular form of composition because the rules relating to its composition were invariable. It is because of this non-flexibility that the canon is so little used as a form at the present time: the modern composer demands a plan of writing that is capable of being varied to such an extent as to give him room for the exercise of his own particular individuality of conception, and this the canon does not do. For this same reason too the fugue and the sonata have successively gone out of fashion and from Schumann down to the present time composers have as it were created their own forms, the difficulty in listening arising from the fact that no one but the composer himself could recognize the form as a form because it had not been adopted to a great enough extent by other composers to make it in any sense universal. The result is that in much present-day music it is very difficult for the hearer to discover any trace of familiar design, and the impression made by such music is in consequence much less definite than that made by music of the classic school. It is probable that a reaction from this state of affairs will come in the near future, for in any art it is necessary that there should be at least enough semblance of structure to make the art work capable of standing as a universal thing rather than as the mere temporary expression of some particular composer or of some period of composition.
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.