Music theory glossary
Every term used on this site, in plain language. Tap a word to jump to its definition.
Tonic
The first degree of a scale and the home chord built on it. Music in C major keeps coming back to C the way a story keeps coming back to its main character.
Supertonic
The second degree of a scale. In C major the supertonic is D, and the ii chord built on it starts most jazz turnarounds.
Mediant
The third degree of a scale, halfway between the tonic and the dominant. In C major the mediant is E.
Subdominant
The fourth degree of a scale and the chord built on it. The move from subdominant to dominant to tonic (IV-V-I) is the most basic journey in Western harmony.
Dominant
The fifth degree of a scale and the chord built on it. A dominant seventh pulls strongly back to the tonic, which is why so many songs end V-I.
Submediant
The sixth degree of a scale, halfway between the tonic and the subdominant an octave up. In C major the submediant is A, home of the relative minor.
Leading tone
The seventh degree of a major scale, a half step below the tonic. It leans into the tonic so strongly that raising it is what makes a minor-key V chord major.
Octave
The distance of twelve semitones, where a note meets itself again with the same letter name. Middle C to the next C is one octave.
Semitone
The smallest step on the piano, from any key to its nearest neighbor. E to F and B to C are the two semitones with no black key between them.
Whole step
Two semitones at once, e.g. C to D. Major scales are built from a fixed pattern of whole and half steps.
Interval
The distance between two notes, named by counting letter names: C to E is some kind of third, C to G some kind of fifth.
Triad
A three-note chord built by stacking two thirds: root, third and fifth. Major, minor, diminished and augmented triads cover nearly all pop harmony.
Seventh chord
A four-note chord made by stacking a seventh on top of a triad. Dominant sevenths, major sevenths and minor sevenths each have their own unmistakable color.
Extended chord
A chord reaching past the octave with ninths, elevenths or thirteenths. Jazz and R&B live here; pop usually stops at the triad.
Root position
A chord with its root as the lowest note. It sounds the most stable and is how chord diagrams are drawn by default.
Inversion
The same chord notes rearranged so a different chord tone is lowest. First inversion puts the third in the bass, second inversion the fifth, and so on.
Voicing
The exact choice of octaves and order for a chord’s notes. The same C major triad can sound mellow or bright depending on how it is voiced.
Close position
A voicing with the chord tones packed as tightly as possible, each a third or less from the next. Most chord diagrams show close position.
Open voicing
A voicing with the notes spread wider than close position, often by dropping one note an octave. Jazz pianists open up seventh chords this way so they ring instead of muddying.
Drop voicing
An open voicing made by taking the second- or third-highest note of a close chord and dropping it an octave. Drop 2 and drop 3 are the two standards.
Slash chord
Chord notation with a bass note after a slash, e.g. C/E. It means: play the chord before the slash, but put the note after it in the bass.
Arpeggio
Playing a chord’s notes one at a time instead of together, usually from low to high. Broken-chord practice and many intros are arpeggiated.
Alberti bass
A left-hand pattern that breaks a chord into root-fifth-third-fifth eighth notes. Classical-era piano is full of it, and it still works under pop ballads.
Stride
A left-hand style that jumps between a low bass note and a chord higher up, oom-pah across the keyboard. The backbone of ragtime and early jazz piano.
Diatonic
Belonging to one key with no outside notes. The six plain triads of C major (C Dm Em F G Am) plus Bdim are its diatonic chords.
Chromatic
Moving by semitones, or using notes from outside the current key. Borrowed chords like bVII in a major key are chromatic.
Accidental
A sharp, flat or natural that alters a note away from the key signature. Each chord page shows exactly which accidentals its notes need.
Enharmonic
Two names for the same key, like C# and Db. Theory picks the spelling that fits the key; the piano key is identical either way.
Key signature
The sharps or flats written at the start of every staff line, telling you the key at a glance. Each scale page shows its key signature.
Relative major and minor
A major key and the minor key sharing its key signature, e.g. C major and A minor. Same notes, different home chord.
Circle of fifths
The twelve keys arranged so each step moves by a fifth. Neighbors share almost all their notes, which is why progressions love traveling around it.
Mode
A scale made by starting the major scale on a different degree. Dorian, Phrygian, Lydian, Mixolydian and Locrian each have their own mood.
Cadence
A chord ending that punctuates music the way commas and periods punctuate sentences. V-I is an authentic cadence, IV-I a plagal one.
Authentic cadence
A V-I (or V-i) ending, the strongest full stop in tonal music. Nearly every song ends on one.
Plagal cadence
A IV-I ending, gentler than an authentic cadence. The “amen” at the end of hymns is the classic example.
Half cadence
A phrase ending on V, which sounds unfinished on purpose. It asks a question the next phrase answers.
Deceptive cadence
A V that resolves somewhere unexpected, usually vi instead of I. The surprise is the whole point.
Tritone
An interval of three whole steps, e.g. B to F. It sounds restless and sits hidden inside every dominant seventh, driving its pull to resolve.
Tritone substitution
Swapping a dominant seventh for the dominant a tritone away (G7 for Db7). The two chords share the same tritone, so the swap keeps the pull but changes the bass.
Secondary dominant
A dominant chord aimed at a chord other than the tonic, like A7 pulling to Dm inside C major. It briefly tonicizes its target.
Borrowed chord
A chord taken from the parallel major or minor key, like the flat-VII in a major key rock song or the major V in a minor key.
Roman numeral analysis
Writing progressions as scale degrees (I-vi-ii-V) instead of letter names, so one analysis covers all twelve keys. Every progression page here uses it.
Nashville numbers
A shorthand where band members call chords by scale degree numbers (1-6m-4-5). Same idea as roman numerals, built for the stage.
Resolution
The move from tension to rest, e.g. a dominant seventh settling onto its tonic. Good voice leading makes resolutions feel inevitable.
Consonance and dissonance
Stable versus restless sounds. Triads are consonant, sevenths and extensions add dissonance, and music breathes by moving between the two.