19. This final note of a key is called its tonic.
20. The major mode is that of keys in which the tonic triad and the two other cardinal triads are major.
21. The minor mode is that of keys in which the tonic triad and one other cardinal triad are minor.
22. A diatonic scale is a series of the notes essential to one major or minor key, arranged in order of pitch and repeating itself in other octaves on reaching the limit of an octave.
23. Modulation is the passing from one key to another.
24. Chromatic notes and chords are those which do not belong to the diatonic scale of the passage in which they occur, but which are not so used as to cause modulation.
25. Enharmonic intervals are minute intervals which never occur in music as directly measured quantities, though they exist as differences between approximately equal ordinary intervals, diatonic or chromatic. In an enharmonic modulation, two chords differing by an enharmonic quantity are treated as identical.
26. Pedal or organ point is the sustaining of a single note in the bass (or, in the case of an inverted pedal, in an upper part) while the harmonies move independently. Unless the harmonies are sometimes foreign to the sustained note, it does not constitute a pedal. In modern music pedals take place on either the tonic or the dominant, other pedal-notes being rare and of complex meaning. Double pedals (of tonic and dominant, with tonic below) are not unusual. The device is capable of very free treatment, and has produced many very bold and rich harmonic effects in music since the earlier works of Beethoven. It probably accounts for many so-called “essential discords.”
In the form of drones the pedal is the only real harmonic device of ancient and primitive music. The ancient Greeks sometimes used a reiterated instrumental note as an accompaniment above the melody. These primitive devices, though harmonic in the true modern sense of the word, are out of the line of harmonic development, and did not help it in any definite way.
27. The fundamental bass of a harmonic passage is an imaginary bass consisting of the roots of the chords.