7.2 Part Writing of Secondary Dominant Chords

Part writing secondary dominants means treating each secondary dominant like a real dominant in its temporary key: resolve the chordal seventh down by step, resolve the raised leading tone up by step, and avoid doubling that leading tone. When you add a bass line to a soprano line, chromatic notes like a raised scale degree often signal a secondary dominant, and the most common pattern is a raised fourth moving up.

Why This Matters for the AP Music Theory Exam

Secondary function shows up across the AP Music Theory exam. You will see multiple-choice questions that test whether you can spot tonicization in notated and performed music, and the free-response section includes harmonic dictation and part-writing tasks where secondary dominants can appear. This topic specifically supports the skill of adding a bass line to a given soprano line using normative 18th-century procedures, so getting comfortable with how chromatic pitches imply a secondary dominant helps you write correct progressions and explain your harmonic choices.

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Key Takeaways

• Treat a secondary dominant exactly like a normal dominant: the chordal seventh resolves down by step, and the temporary leading tone (the raised third of the chord) resolves up by step.
• Do not double the leading tone of a dominant or secondary dominant chord.
• A raised scale degree resolving up by step is a strong clue that tonicization is happening, especially raised 4 moving to 5, which suggests V/V going to V.
• When you harmonize a soprano line, chromatic pitches imply specific secondary dominants, so let the accidentals guide which chord fits.
• Only major or minor triads can be tonicized, so you cannot build a secondary dominant that resolves to a diminished or augmented triad.
• Secondary dominants often appear near cadences and can outline a chromatic bass line like 4 to raised 4 to 5.

Tonicization and Secondary Dominants

Tonicization is a brief, local shift of focus where music borrows notes from another key to make a non-tonic chord sound like a temporary tonic. It does not change the primary key of the piece, and it usually lacks a clear cadence in the new area, which gives it a fleeting quality. The chord being tonicized is the temporary tonic.

For example, in a piece in C major, tonicizing G major means using chords that point to G as a tonic before returning to C major.

The easiest way to spot tonicization in notated music is to look for accidentals that do not belong to the prevailing key. Watch especially for a raised pitch resolving upward by step, which behaves like a leading tone moving to a temporary tonic.

Once you know the temporary tonic, you can identify the chord that led into it. That chord usually has dominant function, meaning it acts as a V or a leading-tone chord in the secondary key.

You can only tonicize major or minor triads, not diminished or augmented triads. In a major key that means vii° cannot be tonicized, and in a minor key ii° cannot be tonicized.

It is most common to tonicize the dominant, the subdominant, or the supertonic (V, IV, ii) of the primary key. For example, in A major the dominant is E major, so the secondary dominant of V would be B major. If you see B major chords appearing in an A major passage, consider that you may be looking at a tonicization.

Secondary Dominants

The chord leading into the temporary tonic is usually a dominant chord because we want listeners to hear the temporary tonic as a tonic. The leading tone in a dominant chord pulls strongly toward its tonic, so the leading tone in a temporary dominant pulls strongly toward the temporary tonic. These temporary dominant chords are called secondary dominants (also called applied dominants).

The most common secondary dominant is V/V, the dominant of the dominant. In C major the dominant is G major, so V/V is D major. Using D major briefly tonicizes G major before the music returns to C major.

Secondary dominants can also tonicize chords other than the dominant. In C major, V/ii uses an A major chord moving to a D minor chord, tonicizing ii. You can also have V/IV, which resolves to the IV chord.

In C major, a V/IV resolving to IV may not add extra accidentals, so it can be hard to tell a I-IV progression from a V/IV-IV progression. Context usually makes it clear. That context might include accidentals in non-chord tones or surrounding chords, such as a B-flat in C major, or stronger emphasis on the tonicized chord.

Secondary dominants commonly appear around cadences and can be chained together to extend a phrase, creating tension and release as the music briefly tonicizes several chords before returning home. Each tonicization in such a chain still needs the right accidentals so the secondary dominant stays a major triad or major-minor seventh chord. Reading the full context matters here, because a chord that looks like a plain I or ii on the surface may actually be functioning as a secondary dominant within a longer progression.

Part Writing Secondary Dominants

When part writing secondary dominants, use the same voice-leading and doubling rules you would use for a normal dominant chord. The temporary leading tone, which is the third of the secondary dominant, resolves up by step, and any chordal seventh resolves down by step. Avoid doubling the leading tone.

Secondary dominants are often written so the raised fourth sits in the bass, which produces a smooth chromatic line. A IV to V6/5 of V to V progression is common because it outlines the bass line 4 to raised 4 to 5, and that chromatic motion sounds clear and strong. When you see a raised 4 moving to 5, you can usually read it as some form of V/V going to V.

When you move from a complete V or V7 in the secondary key, it is acceptable to write an incomplete temporary tonic if it improves the overall progression, but this works best when that tonic is in root position. In that case you typically triple the root and keep a single third to avoid parallel fifths or octaves.

You can write a strong cadence in the secondary key or a weaker one. What matters is that the listener hears the temporary tonic as a tonic, so the resolution should feel cadential, even if it is not a full perfect authentic cadence.

Regular, Irregular, and Deceptive Resolution

When a secondary dominant resolves to the tonic of its secondary key, such as V/V moving to V, this is regular resolution.

If you write a perfect authentic cadence in the secondary key, the temporary tonic sounds very strong, which is useful when moving toward a real modulation. The basic requirements for a perfect authentic cadence still apply:

1. It uses a V chord as the dominant (not vii or vii°). ✅
2. Both chords are in root position. ✅
3. The soprano ends on the tonic. ✅
4. The soprano moves by step into that tonic. ✅

Following these rules means the leading tone of the secondary key appears in the soprano.

You can also write imperfect authentic cadences with secondary dominants, for example when one chord is not in root position. Plagal cadences like IV/V to V are not typically used in tonicizations.

Irregular resolution moves to a substitute for the tonic of the primary key. Examples include V/IV moving to ii6, or vii/V moving to I6/4. These work because a ii6 chord with a doubled third can substitute for IV, and a I6/4 chord often substitutes for V.

Deceptive resolution moves from the V of the secondary key to a chord built on the sixth degree of that secondary key. An example is V6/5/V moving to iii.

How to Use This on the AP Music Theory Exam

Multiple Choice

When a question shows or plays a passage with an unexpected accidental, check whether that accidental is acting as a temporary leading tone resolving up by step. If it is, name the secondary dominant by figuring out the temporary tonic first, then label the chord as V (or V7) of that chord.

Free Response

For tasks that ask you to add a bass line to a given soprano, treat chromatic soprano pitches as clues. A raised 4 moving to 5 strongly suggests V/V going to V, so build a bass line that supports that progression. Keep your voice leading clean: resolve the temporary leading tone up, resolve the chordal seventh down, and do not double the leading tone.

Common Trap

A V/IV in a major key may not require accidentals, so it can look identical to a plain I chord. Use the surrounding harmony and any non-chord-tone accidentals to decide whether tonicization is actually happening before you label it.

Common Misconceptions

• Tonicization is not the same as modulation. Tonicization is a brief local event that does not change the primary key, while modulation establishes a new key with its own cadence.
• A secondary dominant is not just any chromatic chord. It must function as the dominant of the chord it resolves to, which usually means it is a major triad or major-minor seventh chord.
• You cannot tonicize every chord. Only major or minor triads can be tonicized, so there is no secondary dominant resolving to a diminished or augmented triad.
• The chordal seventh of a secondary dominant still resolves down by step. The temporary key does not change how sevenths behave.
• Do not double the temporary leading tone. The same doubling rules that apply to a normal dominant apply here.
• A missing accidental does not always mean no tonicization. A V/IV in major can occur without added accidentals, so you have to read the context.

Related AP Music Theory Guides

• Unit 7 Overview: Harmony and Voice Leading IV (Secondary Function)
• 7.4 Part Writing of Secondary Leading Tone Chords
• 7.1 Tonicization through Secondary Dominant Chords
• 7.3 Tonicization through Secondary Leading Tone Chords