139. _Counterpoint_ is the art of adding one or more parts or melodies to a given melody, the latter being known as the "cantus firmus," or subject. It may therefore be broadly defined as "the art of combining melodies."
The word _counterpoint_ comes from the three words "_punctus contra punctum_," meaning "point against point." The word point as here used refers to the _punctus_--one of the neumae of the mediaeval system, these neumae being the immediate predecessors of modern notes.
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.
[Illustration: 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.