Key relationships describe how one key connects to another based on shared tonic and key signature differences. A parallel key keeps the same tonic but changes mode and signature, closely related keys differ from the original by no more than one accidental, and distantly related keys differ by more than one accidental.
Why This Matters for the AP Music Theory Exam
This topic builds the skill of describing key relationships in both performed and notated music. On the exam you may hear or see a passage move to a new key and need to label that move as relative, parallel, closely related, or distantly related. This connects to listening, score analysis, and your ability to explain how a piece is organized when a section changes key.
You will not be asked to name a specific key by letter from listening alone, but you should be able to describe the type of relationship between two keys.
Key Takeaways
- A parallel key shares the same tonic but uses a different key signature and a different mode (for example D major and D minor).
- A relative key shares the same key signature but starts on a different tonic (for example D major and B minor).
- Closely related keys differ from the original by no more than one accidental, and they are the most common keys a passage shifts to.
- Each major or minor key has a set of closely related keys built from the diatonic major and minor triads of that key.
- Distantly related keys differ by more than one accidental, and parallel keys are a subset of distantly related keys.
- Use the circle of fifths and key-signature comparison to quickly sort closely related from distantly related keys.
Parallel Keys
A parallel key shares the same tonic as the original but has a different key signature. Because the signature changes, the mode changes too, so you move between the major mode and the minor mode while keeping the same starting pitch.
For example, D major has two sharps in its key signature, while D minor has one flat. Their written key signatures differ significantly, which is why parallel keys are not closely related even though they share a tonic.
Composers often use parallel keys to shift the mood of a section. A bright, major passage can switch to its parallel minor for a darker, more introspective feeling, which adds contrast and emotional variety.
Optional modal context: Some textbooks also describe Dorian and Mixolydian as parallel modes when they share a tonic. You will study modes more fully in Unit 8, so treat this only as a connection, not as the core idea here.
Closely Related Keys
Closely related keys are keys whose key signatures differ from the original by no more than one accidental. These are the most common keys to which a passage might shift, because they share many of the same pitches.
Here are two reliable ways to find them.
By accidental count. Look at the original key, then look at the keys with one more and one less accidental, plus the relative key. For an opening tonic of D major (two sharps), the closely related keys are:
- B minor, the relative key (same two sharps)
- A major and F♯ minor, the keys with one additional sharp
- G major and E minor, the keys with one fewer sharp
By diatonic triads. The keys closely related to a given key are those whose tonic triads are the diatonic major and minor triads of the original key. For D major, those are:
- the supertonic key (E minor)
- the mediant key (F♯ minor)
- the subdominant key (G major)
- the dominant key (A major)
- the submediant key (B minor)
Both approaches give you the same set. Relative keys are always a subset of closely related keys.
Quick check: Which keys are closely related to F♯ major?
Distantly Related Keys
Distantly related keys are keys whose key signatures differ from the original by more than one accidental. If a key is not relative and not on the closely related list, it is distantly related.
These keys sit farther apart on the circle of fifths and share fewer pitches, so moving to one can sound more sudden or unstable. Parallel keys are a subset of distantly related keys, which is why D major to D minor counts as a distant relationship even with a shared tonic.
Quick check: Which keys are distantly related to B♭ minor?
Modulation in Context
Modulation is the process of changing from one key to another. Shifting to a closely related key tends to feel smooth and connected, while shifting to a distantly related key creates more contrast and tension.
Composers often pass through closely related keys on the circle of fifths to reach a more distant goal key. This is one way to make a parallel-key shift, such as D minor to D major, feel gradual rather than abrupt. Some composers move directly to a distant key for a striking effect, but that is an artistic choice and not the smoothest path when you are first learning how keys connect.
How to Use This on the AP Music Theory Exam
Listening
When a passage changes key, focus on the relationship rather than the exact letter name. Ask whether the new key keeps the same tonic (parallel), keeps the same signature (relative), feels closely connected (closely related), or feels like a bigger jump (distantly related).
Score Analysis
Compare key signatures directly. If the new signature differs by no more than one accidental, the keys are closely related. If it differs by more than one accidental, they are distantly related. A shared tonic with a different signature points to parallel keys.
Common Trap
Remember that sharing a tonic does not make keys closely related. D major and D minor share a tonic but use different key signatures, so they are distantly related.
Common Misconceptions
- Parallel keys are not closely related. They share a tonic but their signatures differ by more than one accidental, so they are distantly related.
- Relative and parallel are not the same. Relative keys share a key signature with different tonics, while parallel keys share a tonic with different signatures.
- Closely related does not mean only one shared accidental in common pitches. It means the key signature differs by no more than one accidental from the original.
- You do not build a closely related key off the seventh scale degree. The closely related keys come from the diatonic major and minor triads of the original key, not the diminished triad.
- On the listening section you are not expected to name the exact key by letter. You describe the type of key relationship instead.
Related AP Music Theory Guides
Vocabulary
The following words are mentioned explicitly in the College Board Course and Exam Description for this topic.Term | Definition |
|---|---|
accidental | A symbol that modifies the pitch of a note, such as a sharp, flat, or natural. |
closely related keys | Keys whose key signatures differ from the original by no more than one accidental; the most common keys to which a musical passage might shift. |
distantly related keys | Keys whose key signatures differ from the original by more than one accidental. |
dominant key | The closely related key built on the fifth scale degree of the original key. |
key signature | A grouping of sharps or flats presented in a specific order at the beginning of a musical staff that indicates which pitches belong to a particular major or minor scale. |
mediant key | The closely related key built on the third scale degree of the original key. |
parallel key | A key that shares the same tonic as the original key but has a different key signature, such as D major and D minor. |
relative key | A key that shares the same key signature as another key but has a different tonic note; for example, D major and B minor are relative keys. |
subdominant key | The closely related key built on the fourth scale degree of the original key. |
submediant key | The closely related key built on the sixth scale degree of the original key. |
supertonic key | The closely related key built on the second scale degree of the original key. |
tonic | The first scale degree and the primary harmonic center of a key, providing the sense of resolution and stability. |
triads | Three-note chords consisting of a root, third, and fifth. |
Frequently Asked Questions
What is a parallel key?
A parallel key has the same tonic as the original key but a different mode and key signature. For example, D major and D minor are parallel keys because both start on D.
What is a relative key?
A relative key shares the same key signature as the original key but has a different tonic. For example, D major and B minor are relative keys because both use two sharps.
Why do key relationships matter on the AP Music Theory exam?
Key relationships help you describe modulation and organization in performed and notated music. You may need to identify whether a new key is relative, parallel, closely related, or distantly related.