Triads in a key

Build a triad on every degree of the major scale and label its kind with a Roman numeral.

A triad on every degree

Put a snowman on every degree of C major, using only the notes of the scale. You get seven triads, one on each degree I–VII.

Triads on the degrees of C major, from I to I

Count their thirds and you'll find the triads differ:

• major on degrees I, IV and V;
• minor on II, III and VI;
• diminished on VII.

This holds in every major key: in G major the major triads are on G, C and D, the minor ones on A, B and E, the diminished one on F♯.

Practice: The triad on II

Practice: The triad on VII

Practice: Major degrees

Practice: Build the triad

Roman numerals

A triad in a key is labelled with the Roman numeral of its degree. A major triad gets an upper-case numeral (I, IV, V), a minor one lower-case (ii, iii, vi), a diminished one lower-case with a small circle (vii°). One label shows both the degree and the kind of chord.

Triads I, IV and V are called the primary triads: tonic, subdominant and dominant. They can accompany a great many simple melodies.

The primary triads of C major: I – IV – V – I

A Roman numeral does not depend on the key: V in C major is G, B, D; in F major it is C, E, G. The numeral tells the chord's role, not its notes.

Practice: Which degree?

Practice: Triads by ear