240. We now give some episodes suitable for our four-part exposition. Although in actual practice, it is neither necessary nor expedient that all the episodes of a four-part fugue should be in four-part harmony, yet, as the episodes we are now writing are simply meant as illustrations of the method of composition, and as our previous examples have been in three parts, we will write these in four. As before, we begin by completing the last bar of the exposition.
This episode is founded on the first three notes of the subject, treated sequentially in the bass, imitated by inverse movement in the tenor, and accompanied by a semiquaver figure in the upper voices, which is an imitation, partly inverted and partly direct, of the tenor part in the first half bar of the passage.
241. We not infrequently find in fugues that an episode is founded, not on subject or countersubject, but on one of the incidental counterpoints. To illustrate this, we construct our next episode in this way.
