Now this is a melody in the pure song form, such as the earliest popular music contained. But the church composers, the only scientific musicians of the early day, in ignoring that form, as we have seen, developed a scheme of repetition of the identifying parts of their tunes by making the different voices sing them at different times. And this scheme evolved the art of polyphonic writing, which we have seen developed so beautifully by the Netherlands masters and the early Italian church composers. The reader will remember that the principle which lies at the foundation of polyphonic writing is "imitation." After instrumental music began to develop independently it clung for a time to the forms based on imitation, but when the vocal style became dominant in Italy, owing to the enormous popularity of the opera, imitation and its forms fled into Germany, where they found their highest embodiment in instrumental music in the North German fugue. The fugue is the most complex and highly organized polyphonic form we have, and it is necessary that the reader should know something of its construction. A fugue has been defined as "a musical composition developed, according to certain rules of imitation, from a short theme or phrase called the subject. This subject is from time to time reproduced by each of the two, three, four, or more parts or voices for which the fugue is written." The subject, then, is a definite theme, of from four to eight measures, from which the fugue is developed. The next essential part is the answer. This is the first appearance of the subject in one of the subsidiary voices. This appearance is always in the dominant key, and usually has its last notes changed so as to make an ending. The counter-subject is that part of the theme of the first voice which forms the accompaniment to the answer. The announcement of these parts of the fugue is called the exposition. After the exposition the composer works up the melodic ideas of his material in passages of double counterpoint, free imitation, and various other polyphonic devices, all distributed so as to give interest and variety to the fugue, until he reaches the stretto, a portion in which by ingenious changes he brings out a climax, after which he may add a coda (tail-piece) and come to an end. Here is an example by Sir Frederic A. Gore-Ouseley:-- [Music: |-----------|-------Answer------|--Subject--| (Fugue) |--Subject--|--Counter-subject--|----etc.---|]