In AP Music Theory, a common tone is a pitch that two adjacent chords share and that stays in the same voice when the harmony changes. Keeping common tones is a core 18th-century voice-leading move, and it's the preferred way to approach a chordal seventh in four-part writing (PIT-4.A.7).
A common tone is a note that shows up in two chords in a row. For example, in F major the I chord (F-A-C) and the IV chord (Bb-D-F) both contain F. When you part-write that progression, the smoothest option is to keep that F in the same voice instead of jumping it somewhere else. Think of it as the harmonic version of not moving more than you have to. The chord underneath changes, but one voice just stays put, and that anchor makes the whole progression sound connected.
On the AP exam, common tones matter most when seventh chords enter the picture. The CED says chordal sevenths should be approached by common tone or by step (PIT-4.A.7). So if you're writing a ii⁷ chord, the ideal move is for the seventh of the chord to already be sitting in a voice from the previous chord, carried over as a common tone. The CED even names a specific case in PIT-4.A.13: when ii⁷ moves to a cadential ⁶₄, the chordal seventh can be retained in the same voice before it finally resolves down by step. Common tones don't replace resolution rules. They just give you the cleanest on-ramp into a dissonance before the rules kick in.
Common tones live in Topic 4.4 (Voice Leading with Seventh Chords) and Topic 5.3 (Predominant Seventh Chords), supporting learning objectives 4.4.A and 5.3.A, which both ask you to identify and apply 18th-century voice-leading procedures through score analysis, error detection, writing, and listening. Here's the practical payoff. The free-response part-writing questions grade your voice leading, and the single easiest way to avoid errors like parallel fifths, parallel octaves, and awkward leaps is to hold common tones whenever you can. Fewer voices moving means fewer chances to break a rule. When the AP rubric checks how you approached a chordal seventh, common-tone approach is the answer graders are happiest to see.
Keep studying AP Music Theory Unit 5
Visual cheatsheet
view galleryChordal Seventh (Units 4-5)
The chordal seventh is where common tones earn their keep. PIT-4.A.7 says you should approach a seventh by common tone or by step, so the smoothest seventh chords are the ones where the dissonant note was already there in the previous chord and just got reinterpreted.
Voice Leading (Unit 4)
Common-tone retention is rule number one of smooth voice leading. The 18th-century style wants each voice to move as little as possible, and a held common tone is the least movement possible, which is exactly zero.
Predominant Seventh Chords (Unit 5)
Topic 5.3 leans on common tones directly. PIT-4.A.13 lets the seventh of ii⁷ be retained in the same voice when moving to a cadential ⁶₄, a rare case where a chordal seventh gets to wait before resolving down by step.
Parallel Fifths and Parallel Octaves (Unit 4)
Holding a common tone is your best insurance against parallels. A voice that doesn't move can't form parallel fifths or octaves with anything, so common tones quietly eliminate the most-penalized errors on the part-writing FRQs.
You'll use common tones in three ways. First, in part-writing FRQs, where approaching a chordal seventh by common tone is the textbook-correct move and holding common tones keeps you safe from parallel fifths and octaves. Second, in error-detection questions, where a seventh approached by an awkward leap (instead of common tone or step) is exactly the kind of mistake you're asked to spot. Third, in multiple-choice analysis, where you might be asked something concrete like which note the I and IV chords share in F major (it's F). No released FRQ uses the phrase 'common tone' in its prompt, but the part-writing rubric rewards it every single year because it's baked into the voice-leading procedures of LOs 4.4.A and 5.3.A.
They're almost opposites. A tendency tone (like the leading tone or a chordal seventh) has a strong pull and must resolve in a specific direction, usually by step. A common tone is a note that doesn't need to go anywhere because the next chord contains it too. The tricky overlap is that a chordal seventh can arrive as a common tone (held over from the previous chord) but it leaves as a tendency tone, resolving down by step. Same note, two different jobs at two different moments.
A common tone is a pitch shared by two consecutive chords, and good voice leading keeps it in the same voice rather than moving it.
Per PIT-4.A.7, chordal sevenths should be approached by common tone or by step, with leaps allowed only when those options aren't available.
PIT-4.A.13 allows the seventh of ii⁷ to be retained as a common tone into a cadential ⁶₄ before it resolves down by step.
Holding common tones reduces voice motion, which is your best defense against parallel fifths, parallel octaves, and awkward leaps on part-writing FRQs.
Chords whose roots are a fourth or fifth apart share one common tone (like I and IV sharing the tonic), and chords a third apart share two.
A common tone delays motion but never cancels resolution rules; a held chordal seventh still has to resolve down by step eventually.
A common tone is a pitch that appears in two adjacent chords, like the F shared by I (F-A-C) and IV (Bb-D-F) in F major. In four-part writing you usually keep it in the same voice to create smooth voice leading.
No, it's the preferred move, not an absolute rule. The CED requires common-tone or stepwise approach specifically for chordal sevenths (PIT-4.A.7); elsewhere, you can move a common tone to another voice if the texture demands it, as long as you avoid parallels and bad leaps.
A common tone describes a relationship between two chords (a shared note), while a chordal seventh is a specific dissonant chord member that must resolve down by step. They overlap when the seventh is approached by common tone, which is exactly what the AP rubric wants to see.
Yes, in one specific case the CED names. When ii⁷ moves to a cadential ⁶₄, the chordal seventh may be retained in the same voice and then resolve down by step afterward (PIT-4.A.13). The resolution is delayed, not skipped.
Exactly one, the tonic. In F major, I is F-A-C and IV is Bb-D-F, so F is the shared note. Chords with roots a fourth or fifth apart always share one common tone, which is part of why IV works so smoothly as a predominant chord.
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