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With respect to these intervals, the following remarks are to be made:
1st. Any key which we choose to fix upon, may serve as a root or bottom note to all these intervals; and consequently they may take place in all keys and in all octaves.
2ndly. They receive their names from the greater or less distance from their root, and that according to the number of degrees by which they are removed from it. Thus, for example, the third is distant three degrees of the diatonic scale from the lower note or root; the fifth, five degrees; the sixth, six degrees; and so on.
3rdly. The unison (or like sound) is no interval; but it must be so considered in thorough-bass, because two different parts occasionally take one and the same note.
4thly. When we strike intervals separated by still wider distances than the tenth,—as, for example,
such intervals are merely fourths, fifths, sixths,
