Chord Functions: Tonic, Subdominant, Dominant Explained

Published January 24, 2026

Understand why chords move the way they do. Learn the three pillars of harmony: tonic (home), subdominant (away), dominant (tension).

Key Takeaways

Three functions: Tonic (home), Subdominant (away), Dominant (tension).
I, vi, iii = Tonic. IV, ii = Subdominant. V, vii° = Dominant.
The cycle T → SD → D → T creates harmonic narrative.
Substitutions within the same function keep the progression's logic intact.
V-I is the strongest resolution (authentic cadence). V-vi is deceptive.

The Three Pillars of Harmony

Every chord in a key serves one of three functions: Tonic (home), Subdominant (away), or Dominant (tension). Understanding these functions explains why progressions work.

Tonic (I): The home base. Stable, resolved, final. In C major: C, Em, Am (vi also functions as tonic substitute).

Subdominant (IV): Movement away from home. Creates gentle tension. In C major: F, Dm (ii also functions as subdominant).

Dominant (V): Maximum tension. Demands resolution to tonic. In C major: G, G7, Bdim (vii° also functions as dominant).

The Functional Cycle

The most fundamental progression in Western music: Tonic → Subdominant → Dominant → Tonic (I - IV - V - I).

I (home) → IV (departure) → V (tension) → I (return). This cycle creates narrative: stability, departure, crisis, resolution.

The IV-V-I progression is the same cycle starting from the subdominant. The V-I resolution (authentic cadence) is the strongest gravitational pull in harmony.

Chord Substitution Within Functions

Chords sharing the same function can often substitute for each other:

Tonic substitutes: I, vi, iii (all contain the tonic note). In C: C, Am, Em.

Subdominant substitutes: IV, ii (both contain the 4th scale degree). In C: F, Dm.

Dominant substitutes: V, vii° (both contain the leading tone). In C: G, Bdim. V7 (G7) adds the 4th scale degree, doubling the pull to tonic.

This is why vi-IV-I-V works — it cycles through tonic (vi), subdominant (IV), tonic (I), dominant (V).

Practice Exercises

1In the key of G, identify all tonic, subdominant, and dominant function chords. Play I-IV-V-I, then try substitutes (vi for I, ii for IV, vii° for V).
2Analyze a simple song. Label each chord with its function (T, SD, D). Notice how the functions cycle.
3Write a 4-chord progression using one chord from each function category plus a return to tonic.

Common Mistakes

Thinking chord function is only about the root note. It is about the scale degrees the chord contains and its tendency to move.
Using dominant substitutes (vii°) without the leading tone resolving properly.
Ignoring that iii can function as tonic OR dominant depending on context (it contains the leading tone).

Frequently Asked Questions

What is the difference between tonic and dominant?

Tonic is the home chord — stable and resolved. Dominant is the tension chord — unstable and pulling toward tonic. The dominant contains the leading tone (7th scale degree) which wants to resolve up to the tonic.

Why does V7 resolve to I?

V7 contains two tendency tones: the leading tone (7th scale degree) wants to go up to tonic, and the 4th scale degree wants to go down to the 3rd. This dual pull creates maximum tension demanding resolution.

Can I replace a I chord with vi?

Often yes. vi shares two notes with I and functions as a tonic substitute. It sounds more melancholy but still provides resolution. In pop, vi often replaces I in the middle of progressions (e.g., I-V-vi-IV instead of I-V-I-IV).

What is a deceptive cadence?

A deceptive cadence is when V resolves to vi instead of I. It sets up the expectation of V-I (strongest resolution) but diverts to the relative minor. It feels like a surprise or continuation rather than an ending.