89. A minor scale having the same signature as a major scale is said to be its relative minor. E.g.,—e is the relative minor of G, c of E♭, d of F, etc., the small letter being used to refer to the minor key or scale, while the capital letter indicates the major key or scale unless accompanied by the word minor. Relative keys are therefore defined as those having the same signature. G and e are relative keys, as are also A and f♯, etc.
90. A minor scale beginning with the same tone as a major scale is referred to as its tonic minor. Thus, e.g., c with three flats in its signature is the tonic minor of C with all degrees in natural condition; e with one sharp is the tonic minor of E with four sharps, etc. Tonic keys are therefore those having the same key-tone.
91. The eight tones of the diatonic scale (both major and minor) are often referred to by specific names, as follows:
1. Tonic—the tone. (This refers to the fact that the tonic is the principal tone, or generating tone of the key, i.e., it is the tone.)
2. Super-tonic—above the tone.
3. Mediant—midway between tonic and dominant.
4. Sub-dominant—the under dominant. (This name does not refer to the position of the tone under the dominant but to the fact that the fifth below the tonic is also a dominant tone—the under dominant—just as the fifth above is the upper dominant).
5. Dominant—the governing tone. (From the Latin word dominus meaning master.)
6. Super-dominant—above the dominant. Or Sub-mediant—midway between tonic and sub-dominant.