TONIC, in music, signifies a certain degree of tension, or the sound produced by a vocal string in a given degree of tension, or by any sonorous body when put in vibration. It has already been observed in other articles, that the word tone signifies the natural series or succession of the diatonic scale, whether major or minor, or consisting in intervals of both kinds, commencing from any particular note. The tonic therefore, or key, is the sound from whence that series commences; and it is so called, because it establishes the nature of the series, and, as it were, opens a passage to it. With this every piece of music, whether in harmony or melody, for the most part begins, at least when the excluded notes are finished. By excluded notes we mean those notes which are separated from the air by a bar, yet which do not constitute a bar; because they are parts of a time, the rest of which is supposed to have passed before the commencement of the air; and for which, at the end of the strain, there is, or ought to be, always an interval in duration left unoccupied.
Here then we have said, that the air commences for the most part with its tonic or key; that it should end with the same note, is a rule more generally observed, and more necessary to be observed; but that its basis should end upon the tonic, is indispensable. Whatever kind of third the key or tonic has above it, determines the mode. If the third be major, such likewise is the mode; if minor, the mode is also minor. Thus, upon every tonic or key, we may compose in either mode. In short, musicians recognize this peculiarity in the tonic, that the perfect chord does not rigorously belong to any other note except itself. When that chord is struck upon another note, either some dissonance
Tonic
Tonquin. nance is underflood, or some other note becomes the key for that instant.
By this method of transposition, the tonic or key bears the name of C or ut in the major mode, and of A or la in the minor. See Music, Chap. XII.
Tonic, says Rouffean, is likewise the name given by Aristoxenus to one of the three kinds of chromatic music whose divisions he explains, and which was the ordinary chromatic of the Greeks, proceeding by two semi-tones in succession, and afterwards a third minor.
Tonic Dominant. See DOMINANT.