A Dictionary of Music and Musicians/Mediant
MEDIANT (from the Lat. Medius, middle). I. One of the three most significant Regular Modulations of the Ecclesiastical Modes, ranking next in importance to the Dominant, or Reciting-Note. [See Modes, the Ecclesiastical; Modulations, Regular and Conceded.]
The normal position of the Mediant, in the Authentic Modes, lies as nearly as possible midway between the Final and the Dominant. It makes its nearest approach to the fulfilment of this condition, in Modes I, V, IX, and XIII, in which the Dominant is represented by the Fifth of the Scale, and the Mediant, by the Third. In Mode III, the substitution of C for B, in the case of the Dominant, leads to an irregularity: the Mediant is still the Third of the Scale; but, it lies a Third above the Final, and a Fourth below the Reciting-Note. A similar incongruity would arise in the proscribed Mode XI, were it in practical use: for, theoretically, its Final is B, its Dominant G, and its Mediant D. In Mode VII, C is taken for the Mediant, instead of B, in order to avoid forbidden relations with F: the position, therefore, in this case, is, a Fourth above the Final, and a Second below the Dominant.
In the Plagal Modes, the position of the Mediant is governed rather by the necessity for securing a convenient note for the Modulation, than by any fixed law. In Modes II, IV, and X, it is the note immediately below the Dominant: and the same arrangement would take place in the discarded Mode XII, were it in use. In Modes VI, and XIV, it is a Third below the Final. In Mode VIII, it is a Second below the Final; the Second above the Final being sometimes—though not very frequently—substituted for it, in order to avoid forbidden relations with B.
The following Table exhibits, at one view, the Mediants of all the Modes in general use, both Authentic, and Plagal:—
| Mode I. | F. | Mode V. | A. | Mode IX. | C. |
| Mode II. | E. | Mode VI. | D. | Mode X. | B. |
| Mode III. | G. | Mode VII. | C. | Mode XIII. | E. |
| Mode IV. | G. | Mode VIII. | F. | Mode XIV. | A. |
The functions of the Mediant are important, and well defined.
In the Authentic Modes it is constantly used as an Absolute Initial: and, in cases of emergency, it may be so used in the Plagal Modes, also; especially in the VIIIth, in which it frequently occupies that prominent position. By virtue of this privilege, it may appear as the first note of a Plain Chaunt Melody of any kind. In common with the other Regular Modulations, it may begin, or end, any of the intermediate phrases of a Plain Chaunt Melody; and may even begin the last phrase. But, it can never terminate the last phrase. This rule admits of no exception; and is not even broken in those Endings of the Gregorian Tones for the Psalms which close upon the Mediant: for, in these cases, the real close must be sought for in the Antiphon, which immediately follows the Psalm; and this invariably ends upon the Final of the Mode. [See Antiphon; Tones, the Gregorian.]
II. In Modern Music, the term, Mediant, is always applied to the Third of the Scale, by reason of its intermediate position, between the Tonic and the Dominant.
The office of this note is extremely important, inasmuch as it determines whether the Tonality of the Scale is Major or Minor.