Guitar Chord Theory — The Basics
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What is a chord?
A chord is three or more notes played together. On guitar, you press down strings at different frets and strum — the notes ring out as one sound. The type of chord depends on which notes you combine and the gaps (intervals) between them.
The building blocks: intervals
Music is built from 12 semitones (the chromatic scale: C, C#, D, D#, E, F, F#, G, G#, A, A#, B). The distance between any two notes is measured in semitones:
- Minor 2nd — 1 semitone (tense, dissonant)
- Major 2nd — 2 semitones
- Minor 3rd — 3 semitones (sad, bluesy)
- Major 3rd — 4 semitones (bright, happy)
- Perfect 4th — 5 semitones
- Tritone — 6 semitones (dramatic, jazzy)
- Perfect 5th — 7 semitones (stable, powerful)
- Minor 7th — 10 semitones (bluesy, relaxed)
- Major 7th — 11 semitones (dreamy, jazzy)
- Octave — 12 semitones (same note, higher pitch)
Triads: the simplest chords
Most chords start as a triad: a root note plus two others stacked in thirds. The two most common:
- Major chord (e.g. C) — root, major 3rd, perfect 5th (C - E - G). Sounds bright and happy.
- Minor chord (e.g. Cm) — root, minor 3rd, perfect 5th (C - Eb - G). Sounds sad or moody.
Other triads:
- Diminished (e.g. Cdim) — root, minor 3rd, flat 5th. Tense, unstable.
- Augmented — root, major 3rd, sharp 5th. Dreamy, unsettled.
Seventh chords — adding colour
Add a 7th interval on top of a triad and you get richer harmony:
- Major 7th (e.g. Cmaj7) — triad + major 7th. Smooth, jazzy.
- Dominant 7th (e.g. C7) — triad + minor 7th. Bluesy, wants to resolve.
- Minor 7th (e.g. Cm7) — minor triad + minor 7th. Mellow, soulful.
- Minor major 7th (e.g. CmMaj7) — minor triad + major 7th. Cinematic, mysterious.
Suspended chords
A suspended chord replaces the 3rd with a 2nd (sus2) or 4th (sus4). Without the 3rd, the chord is neither major nor minor — it sounds open and unresolved:
- Sus2 (e.g. Csus2) — root, major 2nd, perfect 5th.
- Sus4 (e.g. Csus4) — root, perfect 4th, perfect 5th.
- 9sus4 (e.g. C9sus4) — sus4 with a minor 7th and major 9th. Jazz colour.
Extended chords: 9ths, 11ths, 13ths
Stack more thirds on top of a 7th chord and you get extended chords used heavily in jazz:
- 9th — add the 9th (same as major 2nd, one octave up).
- 11th — add the 11th (same as perfect 4th, one octave up).
- 13th — add the 13th (same as major 6th, one octave up).
These chords are dense and colourful. In practice, some notes (like the 5th or root) are often dropped to keep them playable on guitar.
Altered chords
An altered chord has one or more notes raised or lowered for tension:
- 7#5 (e.g. C7#5) — dominant 7th with a raised 5th.
- 7b5 (e.g. C7b5) — dominant 7th with a lowered 5th.
- 7#9 (e.g. C7#9) — dominant 7th with a raised 9th (the "Hendrix chord").
- 7b9 (e.g. C7b9) — dominant 7th with a lowered 9th.
How to use this
Use the chord & scale player to hear and see every chord type mentioned above. Tap a root note on the left, then tap any chord to hear it and see the guitar diagram. Try the scales wheel to explore melodies over your chords.