An imperfect authentic cadence (IAC) is a dominant-to-tonic cadence (V or vii° to I) that weakens closure by breaking one of the PAC rules, such as putting either chord in inversion, ending the soprano on a note other than the tonic, or substituting vii° for V. It sounds conclusive but not final.
An imperfect authentic cadence is what you get when the harmony says "we're done" but the voicing says "not quite." Like a perfect authentic cadence (PAC), an IAC moves from a dominant-function chord to tonic. The difference is that at least one of the PAC requirements is missing. Maybe the V or I chord is in inversion, maybe the soprano lands on scale degree 3 or 5 instead of the tonic, or maybe a leading-tone chord (vii° or vii°⁷) stands in for V entirely. Any one of those changes downgrades the cadence from "perfect" to "imperfect."
That downgrade is the whole point. An IAC resolves to tonic, so it feels stable, but it leaves enough open that the music wants to keep going. Composers use it mid-phrase or at the end of an antecedent phrase, saving the PAC for the true ending. In AP Music Theory, this lives in Unit 4 alongside the voice-leading procedures in Topic 4.5, where the CED notes that leading-tone seventh chords like vii°⁷ can substitute for V or V⁷ as part of the dominant. When that substitute resolves to tonic, the resulting cadence is authentic but imperfect, since the actual root of V never appears in the bass.
The IAC belongs to Unit 4 (Harmony and Voice Leading I: Chord Function, Cadence, and Phrase) and supports learning objective 4.5.A, which asks you to identify and apply 18th-century voice-leading procedures through score analysis, error detection, writing exercises, and contextual listening. Cadence identification is one of the most reliably tested listening and analysis skills on the exam, and the PAC/IAC distinction is exactly the kind of fine-grained call the test makes you defend. It also matters structurally. Phrase and period analysis depends on cadence strength, since periods are built on a weak-then-strong cadence pattern. If you can't tell an IAC from a PAC, you can't correctly label an antecedent-consequent relationship, and that error cascades through any form question.
Keep studying AP Music Theory Unit 11n6R0KbwwsYCqXY
Authentic Cadence / PAC (Unit 4)
The PAC is the checklist the IAC fails. Both move from dominant to tonic, but a PAC requires root-position V and I with the tonic in the soprano. Memorize the PAC requirements and the IAC defines itself, since breaking any one of them makes the cadence imperfect.
Leading-tone Seventh Chords (Unit 4)
The CED (PIT-4.A.11) says vii°⁷ can substitute for V or V⁷ as part of the dominant. When that substitute resolves to I at a cadence point, the result is an imperfect authentic cadence, because the dominant root never sounds in the bass. This is the direct bridge between Topic 4.5 and cadence labeling.
Phrase and Period Structure (Unit 4)
Period analysis runs on cadence hierarchy. The antecedent phrase ends with a weaker cadence (a half cadence or an IAC) and the consequent answers with a PAC. The IAC's job here is to sound like a comma, not a period, so the listener expects the phrase to continue.
Half Cadence (Unit 4)
Both the IAC and the half cadence create incomplete closure, but for opposite harmonic reasons. A half cadence stops ON the dominant and never resolves. An IAC actually reaches tonic but resolves weakly. Same dramatic effect, completely different Roman numerals.
Cadence identification shows up across multiple-choice listening, score analysis, and the sight-singing and harmonization skills in the free-response section. You'll be asked to label a cadence from notation or by ear, which means checking three things fast. Is the motion V (or vii°) to I? Are both chords in root position? Is the tonic in the soprano? Two yeses and one no means IAC. Practice questions also test the IAC inside double period structures, asking which cadence is stronger at the end of the antecedent group versus the consequent group, and which progression creates the strongest final closure. The expected answer pattern puts the weaker cadence (HC or IAC) earlier and the root-position PAC last. In part-writing FRQs, know that if the prompt or context calls for a conclusive ending, you should write a PAC, not an IAC, so keep V and I in root position and put the tonic in the soprano.
Both are authentic cadences because both resolve dominant to tonic. A PAC has root-position V and root-position I with scale degree 1 in the soprano. An IAC breaks at least one of those conditions, through inversion, a soprano ending on 3 or 5, or a vii° chord substituting for V. The quick test is simple. If everything checks out, it's perfect; if anything is off, it's imperfect. Both are still stronger closure than a half cadence, which never reaches tonic at all.
An imperfect authentic cadence resolves dominant to tonic but misses at least one PAC requirement, such as root-position chords or tonic in the soprano.
There are three common ways a cadence becomes imperfect instead of perfect: an inverted V or I chord, a soprano ending on scale degree 3 or 5, or a vii° or vii°⁷ chord substituting for V.
Per the CED, leading-tone seventh chords can function as dominant substitutes, and when they resolve to tonic at a cadence the result is an IAC.
In period and double period structures, the IAC (or a half cadence) typically ends the antecedent, while the consequent answers with a stronger PAC.
An IAC sounds more conclusive than a half cadence because it actually reaches tonic, but less final than a PAC because the resolution is weakened.
When a part-writing prompt asks for the strongest possible closure, write a root-position PAC, not an IAC.
It's a cadence where a dominant chord (V, V⁷, or a vii° substitute) resolves to tonic, but the closure is weakened because a chord is inverted, the soprano doesn't end on the tonic, or vii° replaces V. It reaches home, just not with full finality.
Yes. Any dominant-to-tonic cadence is authentic. The imperfect label only describes how strongly it closes, not whether the harmonic motion qualifies. PAC and IAC are two strengths of the same cadence type.
An IAC resolves to the tonic chord; a half cadence stops on the dominant and never resolves. Both feel incomplete, but for opposite reasons. The IAC arrives weakly, while the half cadence doesn't arrive at all.
Yes, but only as an imperfect one. The CED states that vii°⁷ can substitute for V or V⁷ as part of the dominant function, so vii° to I is authentic motion. Because the dominant root is missing from the bass, the cadence can never be perfect.
Typically at the end of an antecedent phrase or mid-section, where the music needs a sense of pause without finality. In a double period, exam questions expect the weaker cadence (IAC or HC) earlier and the strongest closure, a root-position PAC, at the very end.