Chapter II.
THE SUBJECT.
24. One of the most important points to be considered in the composition of a fugue is the choice of a good subject. It would be possible to write a fugue of some kind—or, to speak more correctly, a piece in fugal form, on almost any subject that might be selected; but it is by no means every melody that is adapted for fugal treatment; and it is no more possible to make a really good fugue on a bad subject than it would be to make a really good coat out of rotten cloth. In this chapter we shall endeavour to show what are the essentials of a good subject.
25. A Subject has been already defined (§ 8) as "the theme announced in the first instance by any one part or voice without harmony, on which the whole composition is founded." In the overwhelmingly large majority of cases this definition is correct; it is only in fugues with more than one subject, or in fugues with accompaniment, that the subject on its first announcement has any harmony. Many theorists speak of the countersubject (§ 10) as a second subject, and call a fugue with a regular countersubject "a fugue with two subjects," or "a double fugue." In this volume we shall restrict the meaning of the word "subject" to that theme which is announced at the very commencement of the fugue, and speak of a "second" or "third" subject only when such accompanies the first subject before it has been answered in another voice. It is possible also for a second subject to appear later in the fugue, provided it has a separate "exposition" (§ 11) of its own, and is subsequently heard in combination with the first subject.
26. The first point to be considered in writing a fugue subject is clear tonality. This is a matter of the utmost importance, because if we are in any doubt as to our key, it may be very difficult, if not impossible, to give a correct answer, as will be seen in our next chapter. It is quite true that in many of the older fugues the tonality sounds vague and undecided; but this is because they were written in the old church modes, about which, except as a matter of antiquarian curiosity, the student need not trouble himself. It is not necessary that a subject remain throughout in the same key; but if a modulation is made it should be unmistakable, and there should in general be no difficulty in determining where it takes place.
27. It will greatly facilitate the student's labours in this respect if he accustoms himself, when inventing a subject, to think
