Scales, Keys & Modes

Mediant

Pronounced MEE-dee-unt

Definition

The mediant is the third degree of a scale, halfway between the tonic and the dominant: E in C major, C in A minor. It decides whether a key sounds major or minor.

The mediant is scale degree 3. Its name comes from its position: it lies in the middle, halfway between the tonic (degree 1) and the dominant (degree 5). In C major the mediant is E; in A minor it is C. In movable-do solfège it is mi in a major key.

Two treble-clef examples in 4/4. C major: quarter notes C D E F G A B C, numbered 1 to 8, with the word mediant written under E. A minor: A B C D E F G A, numbered 1 to 8, with mediant under C. — The mediant is degree 3: E in C major, a major third above the tonic, and C in A minor, a minor third above.

The note that decides major or minor

Of all seven degrees, the mediant does the most to set a key's mood. In a major key it lies a major third above the tonic (C up to E, four half steps); in a minor key it lies a minor third above (C up to E♭, three half steps). Change that one note and a bright melody turns dark, or the reverse.

Two grand-staff examples in 4/4, two bars each, over a left-hand open fifth C–G in whole notes. First: quarter notes C D E D, then a whole-note C. Second: C D E-flat D, then a whole-note C. — The same phrase over an open fifth (C and G, with no 3rd) in the left hand. With E as the mediant it sounds major; with E♭ it sounds minor.

The same note decides the quality of a chord: the 3rd above a chord's root makes it major or minor. That is why a minor-key piece that ends on a major tonic chord, a device called a Picardy third, sounds suddenly bright.

The mediant chord

The triad on the mediant is minor in a major key (E G B in C major, written iii) and major in natural minor (C E G in A minor, written III). In a major key, iii is one of the less common chords; it shares two notes with both I and V and often moves to vi or IV. In a minor key, III is the tonic chord of the relative major, and moving there, A minor to C major, is one of the most common modulations in minor-key music.

The C major scale numbered by degree, with the mediant, E, in coral.

Mediant relationships

From the 19th century on, composers grew fond of moving between chords whose roots are a third apart but which do not share a key, such as C major to E major or C major to A♭ major. These chromatic mediants keep one common note and shift the others, which gives a bright, unexpected, often magical effect. Film composers use them a great deal.

Common questions

Why is it called the mediant?

Because it lies in the middle, halfway between the tonic (degree 1) and the dominant (degree 5).

What is a chromatic mediant?

A chord whose root is a third away from the chord before it but which does not belong to the same key, such as E major or A♭ major after C major. It keeps one common note and shifts the others, which sounds bright and unexpected.