The tonic chord is the triad built on the first scale degree (I in major, i in minor) that serves as the point of stability and resolution in tonal music; every functional progression on the AP Music Theory exam ultimately departs from and returns to it.
The tonic chord is the triad built on scale degree 1, written as I in a major key and i in a minor key. It's home base. Every other chord in functional harmony is defined by how it relates to the tonic, either pulling toward it (dominant function), setting up that pull (predominant function), or stretching it out (tonic expansion). When a piece ends on the tonic chord, you hear it as finished. When it ends anywhere else, something feels unresolved.
In AP Music Theory, the tonic chord is also a lens for understanding other chords. The CED points out that the mediant triad in a minor key (III) appears most often "in its role as representing the relative major key" (PIT-2.J.3). Translation: when you see III in C minor, that E-flat major triad is really the tonic chord of E-flat major wearing a disguise. So knowing what a tonic chord does helps you decode chords that borrow its job.
The tonic chord lives at the center of Topic 5.4: The iii (III) Chord in Unit 5 (Harmony and Voice Leading II), where learning objective 5.4.A asks you to identify and describe harmonic function and progression in both performed and notated music. You can't describe function without the tonic, because function is literally defined as a chord's relationship to it. Dominant chords resolve to it, predominant chords lead to the dominant that resolves to it, and weak-beat passing chords like iii⁶ exist to expand it. Unit 5's whole project, building logical progressions, starts and ends with I.
Keep studying AP Music Theory Unit 5
Visual cheatsheet
view galleryDominant Chord (Units 4-5)
The dominant (V) is the tonic's opposite number. V creates tension because its leading tone wants to resolve up to scale degree 1, and the V-I motion is the strongest gesture in tonal music. You can't have a dominant without a tonic to resolve to, which is why the authentic cadence (V-I) is the genre's default ending.
The iii (III) Chord (Unit 5)
In a minor key, III is the tonic chord of the relative major in disguise. The CED (PIT-2.J.3) says the mediant rarely shows up as a functional chord in 18th-century style; when it does appear in minor, it usually signals a shift toward the relative major key. Recognizing 'tonic behavior' is how you catch that move.
Functional Harmony (Unit 5)
Functional harmony sorts every chord into tonic, predominant, or dominant jobs. The tonic chord is the reference point for the whole system. The standard progression model (tonic → predominant → dominant → tonic) is just a round trip away from home and back.
Scale Degree (Unit 1)
The tonic chord is a Unit 1 idea grown up. 'Tonic' starts as the name for scale degree 1, the note a scale is built on. Stack a third and a fifth on top of it and you get the tonic chord. Same home-base concept, just expanded from a single pitch to a triad.
The tonic chord shows up constantly, even when the question isn't 'about' it. Multiple-choice questions ask you to identify harmonic function in notated and performed music (LO 5.4.A), and that means recognizing tonic arrivals, tonic expansions, and chords that substitute for or represent the tonic. Practice questions in this area test details like which inversion iii and IV typically take during tonic expansion (first inversion, on weak beats) and which major key the III chord represents in minor (the relative major). On the free-response side, the part-writing and harmonization FRQs require you to begin and end progressions sensibly, which almost always means anchoring to I or i. If your Roman numeral analysis or figured bass realization treats the tonic wrong, the whole progression falls apart.
The tonic chord is built on scale degree 1 of the current key; the III chord is built on scale degree 3. The confusion happens in minor keys, where III is a major triad whose root is the tonic of the relative major (E-flat major in C minor, for example). III can sound like a tonic, but it's the tonic of a different key. Per PIT-2.J.3, that representative role is its main use, since the mediant rarely functions on its own in 18th-century-style progressions.
The tonic chord is the triad built on scale degree 1, written I in major keys and i in minor keys, and it serves as the point of rest and resolution in tonal music.
All harmonic function is defined relative to the tonic: dominant chords resolve to it, predominant chords lead toward the dominant, and the standard progression travels tonic → predominant → dominant → tonic.
In a minor key, the III chord usually acts as a representative of the relative major key's tonic rather than as an independent functional chord (PIT-2.J.3).
During tonic expansion, chords like iii⁶ and IV⁶ typically appear in first inversion on weak beats to prolong the tonic without leaving home.
On the exam, identifying tonic arrivals and expansions is core to LO 5.4.A, which asks you to describe harmonic function in both performed and notated music.
It's the triad built on the first scale degree of a key, labeled I in major and i in minor. It functions as the home base that progressions depart from and resolve back to, which is why pieces in common practice style typically begin and end on it.
No. The tonic chord matches the key's quality, so it's a major triad (I) in a major key and a minor triad (i) in a minor key. In C minor, the tonic chord is C-E♭-G, a minor triad.
The tonic chord sits on scale degree 1 of your current key, while III sits on scale degree 3. In minor, III is the tonic triad of the relative major key, so it can feel tonic-like, but per the CED it mostly appears as a representative of that relative major, not as a functional chord in its own right.
The tonic is a single pitch, scale degree 1 (like C in C major). The tonic chord is the full triad built on that pitch (C-E-G). The exam uses both terms, so read carefully whether a question is asking about a note or a chord.
It appears in harmonic function questions tied to LO 5.4.A, where you identify progressions in performed and notated music, and in part-writing FRQs where progressions need to start and end logically on the tonic. Questions also test tonic expansion details, like iii and IV appearing in first inversion on weak beats.
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