Construct and label triads and seventh chords, and explain how they function within a key using Roman numerals and figured bass

What this dot point is asking

You need to build and label any triad or seventh chord, identify its inversion, and explain how chords function inside a key. This connects directly to analysis and to harmonising melodies in composition.

Building triads

Take a root, add the note a third above, then the note a fifth above the root. The quality depends on the two stacked thirds:

• Major triad: major third then minor third (C E G).
• Minor triad: minor third then major third (C E flat G).
• Diminished triad: two minor thirds (C E flat G flat).
• Augmented triad: two major thirds (C E G sharp).

Seventh chords

Adding a fourth note a third above the fifth makes a seventh chord. The most important is the dominant seventh (V7), built on the fifth degree: a major triad plus a minor seventh (G B D F in C major). Its built-in tritone (between the third and seventh) creates strong pull back to the tonic, which is why V7 to I is the most decisive progression in tonal music. Other common types are the major seventh, minor seventh and half-diminished seventh.

Inversions and figured bass

When a note other than the root is in the bass, the chord is inverted. Figures show this:

• Root position (5/3), often unmarked.
• First inversion (6/3, usually just 6): the third is in the bass.
• Second inversion (6/4): the fifth is in the bass.

For seventh chords the figures are 7, 6/5, 4/3 and 4/2 for root position through to third inversion. Roman numerals combine with these figures, so a first-inversion tonic in C is written I6 (or Ib).

Function and progression

Chords group into functions. The tonic (I, and often vi) gives stability and rest. The dominant (V, V7, vii) creates tension that wants to resolve to the tonic. The subdominant or pre-dominant (IV, ii) moves the music away from the tonic and sets up the dominant. A huge amount of tonal music follows the path tonic to pre-dominant to dominant to tonic.

Cadences

A cadence is the harmonic punctuation at the end of a phrase:

• Perfect (authentic): V to I, a full stop.
• Plagal: IV to I, the gentle amen.
• Imperfect (half): ends on V, a comma that needs continuation.
• Interrupted (deceptive): V to vi, a surprise that avoids the expected resolution.

Recognising cadences by ear and on the page is a common aural and analysis task.

Why this matters

Harmony underpins the whole course. In analysis you label progressions and cadences to explain how a piece is organised. In composition and arranging you choose chords to support a melody and create direction. In the aural test you must hear whether a chord is major or minor and whether a cadence is perfect or interrupted. Drill triad qualities in every key, then practise hearing I, IV and V in real recordings until the functions are obvious.