A one-page visual summary of Secondary Function — every tonicization rule, secondary dominant, and secondary leading-tone chord you need to know for the exam, on a single screen.
What it covers: Borrowing the dominant's pull for a non-tonic chord — tonicization, secondary dominant chords, secondary leading-tone chords, and correctly part-writing both.
Exam weight: AP Music Theory is weighted by section, not by unit (45% multiple choice, 45% free response, 10% sight-singing). Secondary function is one of the most heavily tested harmonic-analysis skills on the free-response section.
The big question: How does borrowing a dominant or leading-tone chord from another key temporarily "tonicize" a chord without actually changing keys?
Big Ideas covered: Pitch (BI 1), Music Design (BI 4).
Key topics at a glance
Tonicization
Briefly treating a non-tonic chord as if it were its own tonic, usually signaled by a chromatically raised leading tone.
Secondary (Applied) Dominant
V/x or V7/x — the dominant chord borrowed from the key of chord x, inserted right before it. Most common: V/V.
Spelling a Secondary Dominant
Build a major triad (or Mm7) a perfect 5th above the target chord's root, raising the third to create a new leading tone.
Secondary Dominant Resolution
The borrowed leading tone resolves up a half step to the target root; the chordal 7th (if present) resolves down by step — same rules as any V(7).
Secondary Leading-Tone Chord
vii°/x or vii°7/x — a diminished triad or seventh borrowed from the key of chord x, built a half step below its root.
Which Chords Can Be Tonicized
Any major or minor diatonic triad (commonly V, ii, vi, IV) — not a diminished triad like vii°.
Tonicization ≠ Modulation
Tonicization is brief (one chord or short passage); the overall key never changes. A true modulation establishes a new key for a sustained passage.
Spotting Secondary Function in a Score
Look for a chromatic pitch not in the key signature that resolves like a leading tone into the following chord.
The key terms you must know
Tonicization — briefly treating a non-tonic chord as if it were tonic.
Secondary (applied) dominant — a V or V7 borrowed from the key of a non-tonic chord to tonicize it.
V/V (secondary dominant of the dominant) — the most common secondary dominant, tonicizing V.
Secondary (applied) leading-tone chord — a diminished triad or seventh borrowed from a non-tonic chord's key.
vii°/x, vii°7/x — the labels for a secondary leading-tone triad or fully-diminished seventh chord.
Borrowed leading tone — the chromatically raised pitch that creates the tonicizing pull; resolves up by step.
Applied chord — another name for a secondary dominant or secondary leading-tone chord.
Chromatic alteration — a pitch outside the key signature, often signaling secondary function.
Key themes to remember
Secondary function borrows, it doesn't modulate. The overall key stays the same; only one chord briefly feels like tonic.
Only major/minor triads can be tonicized. A diminished triad (like vii°) can't be treated as a temporary tonic.
The borrowed leading tone still resolves up. Chromatic alterations in secondary chords follow the same tendency-tone rules as any leading tone.
Dominant or diminished — same job, different color. Secondary dominants and secondary leading-tone chords both tonicize; they just use different chord qualities.
Look for the accidental. A chromatic note not in the key signature is your first clue that secondary function is happening.
Common exam traps
Don't confuse tonicization with modulation. If it's just one chord (or a couple), it's tonicization — modulation requires a sustained new key area.
V/V is not the same as V of the original key. It contains a chromatic alteration and functions as the dominant of the dominant, not of tonic.
Don't try to tonicize a diminished chord. vii° (or ii° in minor) cannot be the target of a secondary dominant in standard practice.
The borrowed leading tone must resolve correctly. Forgetting to resolve it up by step is a common voice-leading error with secondary chords.
Read the label direction correctly. V/ii means "the dominant OF ii," not "ii of V" — the chord after the slash is the target being tonicized.