# Chord function

*Module 8 · Lesson 4: Harmony in a key · BazzLow*

> Group chords by their role (tonic, subdominant, dominant) and understand tension and release.

Before this lesson: [8.3 Chords of a minor key](https://bazzlow.com/en/harmony-in-a-key/minor-key-chords/)

Chords in a key do not all do the same job. Some feel like home, some lead away, and some create tension. Knowing which is which tells you where a progression is going.

## Three groups

Chords in a key fall into three **functional groups**. The tonic group is home (the **tonic function**); the subdominant group moves away and prepares, which is why it is also called **predominant**; the dominant group has tension and wants to resolve.

*The three functional groups in a major key, with the chords of C.*

|  | Tonic | Subdominant | Dominant |
| --- | --- | --- | --- |
| Function | T | S | D |
| Chords | I, vi, iii | IV, ii | V, vii° |
| In C | C, Am, Em | F, Dm | G, B° |
| Feeling | home, rest | moving away, preparing | tension, wanting to resolve to I |

Chords in the same group share notes and can often replace each other: vi shares two notes with I, and ii shares two notes with IV. The iii chord is the least clear-cut: it shares notes with both I and V, and different books classify it differently. It is grouped with tonic here, as in the Key Chords tool.

## Tension and release

The typical motion is **T → S → D → T**: leave home, prepare, build **tension**, come back in a **release**. Many common progressions are this cycle (lesson 8.5). The dominant pulls to the tonic because it contains the leading tone (7, a half step below the tonic) and, as a V7, the tritone (Module 10).

## Root movements

The **root movement** between chords has a strength:

- **down a 5th** (= up a 4th): V→I, ii→V, vi→ii. The strongest;
- by step: IV→V;
- by 3rd: I→vi, the weakest change, because the two chords share notes.

In minor keys the groups are the same: i (and III, VI) tonic, iv and ii° subdominant, V and vii° dominant. VI can also act as a predominant before V.

> For the bass: the bass line plays the roots of these movements. The bass is the voice that makes a progression sound strong or weak.

## Try it

In C, play roots in the order T–S–D–T in different ways (C F G C, C Dm G C, Am F G C) and listen for the moment of tension on G.

## New terms

- chord function
- tonic function
- subdominant function
- predominant
- dominant function
- tension
- release
- root movement

Page: https://bazzlow.com/en/harmony-in-a-key/chord-function/