in Music, (from the Latin fuga, "a chase"), a piece of music sometimes longer and sometimes shorter, in which, agreeable to the rules of harmony and modulation, the composer treats a subject; or, in other words, what expresses the capital thought or sentiment of the piece, in causing it to pass successively and alternately from one part to another.
These are the principal rules of the fugue; of which some are peculiar to itself; and others common to it with what the French call imitation.
1. The subject proceeds from the tonic to the dominant, or from the dominant to the tonic, in rising or descending.
2. Every fugue finds its response in the part immediately following that which commenced.
3. That response ought to resume the subject in the interval of a fourth or fifth above or below the key, and to pursue it as exactly as the laws of harmony will admit; proceeding from the dominant to the tonic when the subject is introduced from the tonic to the dominant, and moving in a contrary direction when the subject is introduced from the dominant to the tonic. One part may likewise resume the same subject in the octave or unison of the preceding; but in that case, it is a repetition rather than a real response.
4. As the octave is divided into two unequal parts, of which the one contains four gradations descending from the tonic to the dominant, and the other only three in continuing the ascent from the dominant to the tonic; this renders it necessary to have some regard to this change in the expression of the subject, and to make some alterations in the response, that we may not quit the cords that are essential to the mode. It is a different case when the composer intends to alter the modulation; for there the exactness of the response itself, when taken in a different tone, produces the alteration proper for this change.
5. It is necessary that the fugue should be planned in such a manner, that the response may commence before the close of the first air, so that both the one and the other may be in part heard at the same time: that, by this anticipation, the subject may be as it were connected with itself, and that the art of the composer may discover itself in this concourse. It is absolute mockery, instead of a fugue, to impose upon the hearers the same air, merely transposed from one key to another, without any other restraint than an accompaniment afterwards formed at pleasure. This deserves at best no better name than what the French call imitation. See Imitation.
Besides these rules, which are fundamental, there are others which, though prescribed by taste alone, are not less essential. Fugues, in general, render music more noisy than agreeable; it is for this reason that they are more agreeable in the chorus than anywhere else. Now, as their chief merit consists in fixing the ear on the principal air or subject, which for this reason is made to pass incessantly from part to part, and from mode to mode, the composer ought to exert his care in preserving that air always distinct; or to prevent it from being absorbed in, or confounded with, the other parts. To produce this effect, there are two different ways; one in the movement, which must be incessantly contrasted with itself; so that, if the procedure of the fugue be accelerated, the other parts move gravely and with protracted notes; or, on the contrary, if the motion of the fugue be slow and solemn, the accompaniments must have more and quicker business. The other method is to extend the harmony, by removing the parts at a greater distance one from the other; lest the others, too nearly approximated to that which contains the subject, should be confounded with it, and prevent it from being distinguished with sufficient clearness; so that what would be an imperfection anywhere else, becomes here a beauty.
The unity of melody should be preserved: this is the great and general rule, which must frequently be practised by different means. The cords must be chosen, and the intervals, so that one particular sound may produce the same effect; this can only result from the unity of the melody. It will sometimes be necessary to employ voices and instruments of different kinds, that the parts which ought to prevail may be most easily distinguished; this again shows the necessity of preserving the unity of the melody. Another object of attention, no less necessary, is, in the different connections of modulation which are introduced by the procedure and progress of the fugues, to cause all these modulations to correspond at the same time in all the parts, to connect the whole in its progress by an exact conformity of modes: lest, if one part be in one mode, and another in another, the general harmony should be in none at all, and for that reason should no longer be able to produce simple effects upon the ear, nor simple ideas in the mind; which is another reason for preserving unity of melody. In a word, in every fugue the confusion of melodies and modulations is at once what a composer has most to fear, and will find the greatest difficulty in avoiding; and as this kind of music never produces a pleasure above mediocrity, one may say that a fine fugue is, though the masterpiece of an excellent harmonist, ungrateful to his toil. There are still several other kinds of fugues; such as the perpetual fugue*, the double fugue, the inverted fugue.
The inverted fugue is a manner of composition, in which the flying part proceeds in a contrary direction to the other fugue, which had been formerly fixed in the same piece of music. Thus, when the first fugitive part is heard in ascending from the tonic to the dominant, or from the dominant to the tonic, the counter fugue ought to be heard in descending from the dominant to the tonic, or from the tonic to the dominant, and vice versa. Its other rules are exactly like those of the common fugue.