CANON, in modern music, is a kind of fugue, which they call a perpetual fugue, because the different parts beginning one after another, repeat incessantly the same air.
Formerly, says Zarlino, they placed, at the head of perpetual fugues, particular directions which showed how this kind of fugues was to be sung; and these directions being properly the rules by which perpetual fugues were composed were called canoni, rules or canons. From this custom, others taking the title for the thing signified, by a metonymy, termed this kind of composition canon. Such canons as are composed with the greatest facility, and of consequence most generally used, begin the fugue either with the octave or the unison; that is to say, that every part repeats in the same tone the melody of the preceding. In order to form
Canon. form a canon of this kind, it is only necessary for the composer to make an air according to his taste; to add in score as many parts as he chooses, where the voices in octave or uniform repeat the same melody; then forming a single air from all these parts successively executed, to try whether this succession may form an entire piece which will give pleasure, as well in the harmony as the melody.
In order to execute such a canon, he who sings the first part begins alone, and continues till the air is finished; then recommences immediately, without any suspension of sound or interruption of time; as soon as he has ended the first couplet, which ought to serve for the perpetual subject upon which the whole canon has been composed, the second part begins and repeats the same couplet, whilst the first who had begun pursues the second: others in succession begin, and proceed the same way, as soon as he who precedes has reached the end of the first couplet. Thus, by incessantly recommencing, an universal close can never be found, and the canon may be repeated as long as the singers please.
A perpetual fugue may likewise consist of parts which begin with the intervals of a fourth or fifth; or, in other words, every part may repeat the melody of the first, a fourth or a fifth higher or lower. It is then necessary that the whole canon should be invented di prima intensione, as the Italians say; and that sharps or flats should be added to the notes, whose natural gradations do not answer exactly, by a fourth or fifth, to the melody of the preceding part, and produce the same intervals with itself. Here the composer cannot pay the least regard to modulation; his only care is, that the melody may be the same, which renders the formation of a canon more difficult; for at every time when any part resumes the fugue, it takes a new key; it changes the tone almost at every note, and what is still worse, no part is at the same time found in the same tone with another; hence it is that this kind of canons, in other respects far from being easy to be perused, never produces a pleasing effect, however good the harmony may be, and however properly it may be sung.
There is a third kind of canon, but very scarce, as well because it is extremely difficult, as because it is for the most part incapable of giving pleasure, and can boast no other merit but the pains which have been thrown away in its composition. This may be called a double canon inverted, as well by the inversions which are practised in it with respect to the melody of the parts, as by those which are found among the parts themselves in singing. There is such an artifice in this kind of canon, that, whether the parts be sung in their natural order, or whether the paper in which they are set be turned the contrary way, to sing them backward from the end to the beginning, in such a manner that the bass becomes the upper part, and the rest undergo a similar change, still you have pretty harmony, and still a regular canon. The reader may consult Rousseau's Dictionary in this article, where he is referred to Plate D. fig. 11. for two examples of canons of this sort extracted from Bontempi, who likewise gives rules for their composition. But he adds, that the true principle from which this rule is deduced will be found at the word Système, in his account of
the system of Tartini, to which we must likewise once more refer the reader; as a quotation of such length must have protracted our article to an enormous extent.
To form a canon in which the harmony may be a little varied, it is necessary that the parts should not follow each other in a succession too rapid, and that the one should only begin a considerable time after the other. When they follow one another so immediately as at the distance of a semibreve or a minim, the duration is not sufficient to admit a great number of chords, and the canon must of necessity exhibit a disagreeable monotony; but it is a method of composing, without much difficulty, a canon in as many parts as the composer chooses. For a canon of four bars only, will consist of eight parts if they follow each other at the distance of half a bar; and by each bar which is added, two parts will constantly be gained.
The emperor Charles VI. who was a great musician, and composed extremely well, took much pleasure in composing and singing canons. Italy is still replete with most beautiful canons composed for this prince, by the best masters in that country. To what has been said by Rousseau, we need only subjoin, that the English catch and the Italian canon are much the same; as any intelligent reader may perceive, from comparing the structure and execution of the English catch with the account of canons which has now been given.