---
title: "Locrian Mode — AP Music Theory Definition & Exam Guide"
description: "Locrian is the 7th diatonic mode, built on ti with a diminished 5th above its tonic. Learn how to spell it, hear it, and spot it on the AP Music Theory exam."
canonical: "https://fiveable.me/ap-music-theory/key-terms/locrian"
type: "key-term"
subject: "AP Music Theory"
unit: "Unit 8"
---

# Locrian Mode — AP Music Theory Definition & Exam Guide

## Definition

Locrian is the seventh mode of the diatonic scale, built on the seventh degree (ti) of the major scale. It is the only mode with a diminished fifth above its tonic, which makes its tonic triad diminished and gives it an unstable, dissonant sound rarely used as a home key.

## What It Is

Locrian is what you get when you play all the [notes](/ap-music-theory/unit-1/rhythmic-values/study-guide/U8CmLtTY0617W10Qwt6B "fv-autolink") of a [major scale](/ap-music-theory/key-terms/major-scale "fv-autolink") but start and end on scale degree 7 (ti). Play C major's white keys from B to B and you have B Locrian. Same pitches, totally different center of gravity. Its interval pattern is half-whole-whole-half-whole-whole-whole, which puts a half step right at the start and, more importantly, a **diminished fifth** between the tonic and the fifth scale degree.

That diminished fifth is the whole story. Every other [diatonic](/ap-music-theory/unit-1/major-keys-key-signatures/study-guide/fWrNAPRn7Np3XtWm1p4w "fv-autolink") mode has a perfect fifth above its tonic, so its tonic triad is major or minor and sounds like a stable home base. Locrian's tonic triad is diminished (in B Locrian, that's B-D-F), and a diminished chord sounds like it needs to resolve somewhere else. A mode whose 'home' chord refuses to feel like home is hard to write in, which is why Locrian is the rarest mode in Western music. A useful shortcut for spelling it is to think of natural minor with a lowered 2nd and a lowered 5th.

## Why It Matters

Modes live in [Unit 1](/ap-music-theory/unit-1 "fv-autolink") of [AP Music Theory](/ap-music-theory "fv-autolink") alongside scales, key signatures, and intervals. The CED expects you to know all seven diatonic modes (Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, Locrian), and Locrian is the one with the most distinctive fingerprint. If you can explain *why* Locrian is unstable, you're really demonstrating two bigger Unit 1 skills at once. You're showing you can build a scale from a pattern of whole and half steps, and you can hear how interval quality (a diminished fifth instead of a perfect fifth) changes the character of everything built on top of it. Locrian is also a great memory anchor for the full mode list, since it always comes last and always starts on ti.

## Connections

### [Mode (Unit 1)](/ap-music-theory/key-terms/mode)

Locrian is one of the seven diatonic modes, each built by starting the same set of pitches on a different [scale degree](/ap-music-theory/key-terms/scale-degree "fv-autolink"). Knowing the order (Ionian through Locrian) lets you generate any mode from a major scale you already know.

### [Diminished Fifth (Unit 1)](/ap-music-theory/key-terms/diminished-fifth)

The [diminished fifth](/ap-music-theory/key-terms/diminished-fifth "fv-autolink") between Locrian's tonic and fifth scale degree is its defining interval. This is the same tritone you'll later see driving dominant seventh chords toward resolution, which is exactly why Locrian never feels resolved.

### [Diatonic Scale (Unit 1)](/ap-music-theory/key-terms/diatonic-scale)

Locrian uses the exact pitches of a diatonic (major) scale with no alterations. B Locrian and C major are the same seven notes; only the [tonic](/ap-music-theory/key-terms/tonic "fv-autolink") changes. That's the core idea of rotation that all modes share.

### [Lydian (Unit 1)](/ap-music-theory/key-terms/lydian)

Lydian and Locrian are the two 'tritone modes.' Lydian has an augmented fourth above its tonic, Locrian has a diminished fifth. Same dissonant interval, but Lydian keeps a perfect fifth so it still sounds stable, while Locrian doesn't.

## On the AP Exam

Modes show up on the multiple-choice section, both aurally and in notation. You might hear a melody and identify its mode, see a scale written out and name it, or be asked to spell a mode starting on a given pitch. For Locrian specifically, the giveaway is the diminished fifth above the tonic (and the half step right above it). Two fast strategies work. By notation, find the parent major scale: if the tonic is the leading tone of that key, it's Locrian. By ear, listen for a tonic that sounds tense and unresolved instead of settled. No released FRQ has centered on Locrian, but mode identification is fair game in MCQs, and the interval skills behind it (recognizing a diminished fifth, building scales from step patterns) run through the entire exam.

## Locrian vs Phrygian

Phrygian and Locrian both start with a half step above the tonic (a lowered 2nd compared to natural minor), so they're easy to mix up by ear and on paper. The difference is the fifth. Phrygian has a perfect fifth above its tonic, so its tonic triad is minor and stable. Locrian has a diminished fifth, so its tonic triad is diminished. If the 2nd is lowered, check the 5th: perfect means Phrygian, diminished means Locrian.

## Key Takeaways

- Locrian is the seventh diatonic mode, built by starting a major scale on scale degree 7 (ti), so B Locrian uses the same pitches as C major.
- It is the only diatonic mode with a diminished fifth above its tonic, which makes its tonic triad diminished.
- Because its tonic triad is diminished and unstable, Locrian is the rarest mode as a basis for actual pieces of music.
- A quick way to spell Locrian is to take natural minor and lower both the 2nd and 5th scale degrees.
- To tell Locrian from Phrygian, check the fifth above the tonic: Phrygian's is perfect, Locrian's is diminished.
- Its step pattern is half-whole-whole-half-whole-whole-whole, with that opening half step as an immediate red flag in notation.

## FAQs

### What is the Locrian mode in music theory?

Locrian is the seventh mode of the diatonic scale, built on the seventh degree of a major scale. B Locrian uses the exact notes of C major (B-C-D-E-F-G-A) but treats B as the tonic, creating a diminished fifth between B and F.

### Why is Locrian considered unstable?

Its tonic triad is diminished because of the diminished fifth above the tonic. A diminished chord sounds like it needs to resolve, so the 'home' of a Locrian piece never actually feels like home.

### Is Locrian ever actually used in real music?

Rarely, which is why the CED definition you'll see calls it the least common mode. It appears in some jazz and experimental music, but it almost never serves as a stable key center the way Dorian or Mixolydian can.

### What's the difference between Locrian and Phrygian?

Both have a lowered 2nd scale degree, so they sound similar at the start. Phrygian keeps a perfect fifth above the tonic and has a minor tonic triad, while Locrian's fifth is diminished and its tonic triad is diminished. The fifth is the tiebreaker.

### How do I find the Locrian mode on a given note for the AP exam?

Treat the given note as ti and work backward to the major scale a half step above it. F is the leading tone of G-flat major, so F Locrian uses G-flat major's pitches starting on F. Alternatively, write natural minor on that note and lower the 2nd and 5th.

## Related Study Guides

- [Unit 8 Overview: Modes and Form](/ap-music-theory/unit-8/review/study-guide/azh0orlEVNX2vpDvh1Ld)

## Structured Data

```json
{"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/ap-music-theory/key-terms/locrian#resource","name":"Locrian Mode — AP Music Theory Definition & Exam Guide","url":"https://fiveable.me/ap-music-theory/key-terms/locrian","learningResourceType":"Concept explainer","educationalLevel":"AP / High School","about":{"@id":"https://fiveable.me/ap-music-theory/key-terms/locrian#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-06-11T00:50:11.171Z","isPartOf":{"@type":"Collection","name":"AP Music Theory Key Terms","url":"https://fiveable.me/ap-music-theory/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/ap-music-theory/key-terms/locrian#term","name":"Locrian","description":"Locrian is the seventh mode of the diatonic scale, built on the seventh degree (ti) of the major scale. It is the only mode with a diminished fifth above its tonic, which makes its tonic triad diminished and gives it an unstable, dissonant sound rarely used as a home key.","url":"https://fiveable.me/ap-music-theory/key-terms/locrian","inDefinedTermSet":{"@type":"DefinedTermSet","name":"AP Music Theory Key Terms","url":"https://fiveable.me/ap-music-theory/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is the Locrian mode in music theory?","acceptedAnswer":{"@type":"Answer","text":"Locrian is the seventh mode of the diatonic scale, built on the seventh degree of a major scale. B Locrian uses the exact notes of C major (B-C-D-E-F-G-A) but treats B as the tonic, creating a diminished fifth between B and F."}},{"@type":"Question","name":"Why is Locrian considered unstable?","acceptedAnswer":{"@type":"Answer","text":"Its tonic triad is diminished because of the diminished fifth above the tonic. A diminished chord sounds like it needs to resolve, so the 'home' of a Locrian piece never actually feels like home."}},{"@type":"Question","name":"Is Locrian ever actually used in real music?","acceptedAnswer":{"@type":"Answer","text":"Rarely, which is why the CED definition you'll see calls it the least common mode. It appears in some jazz and experimental music, but it almost never serves as a stable key center the way Dorian or Mixolydian can."}},{"@type":"Question","name":"What's the difference between Locrian and Phrygian?","acceptedAnswer":{"@type":"Answer","text":"Both have a lowered 2nd scale degree, so they sound similar at the start. Phrygian keeps a perfect fifth above the tonic and has a minor tonic triad, while Locrian's fifth is diminished and its tonic triad is diminished. The fifth is the tiebreaker."}},{"@type":"Question","name":"How do I find the Locrian mode on a given note for the AP exam?","acceptedAnswer":{"@type":"Answer","text":"Treat the given note as ti and work backward to the major scale a half step above it. F is the leading tone of G-flat major, so F Locrian uses G-flat major's pitches starting on F. Alternatively, write natural minor on that note and lower the 2nd and 5th."}}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"AP Music Theory","item":"https://fiveable.me/ap-music-theory"},{"@type":"ListItem","position":2,"name":"Key Terms","item":"https://fiveable.me/ap-music-theory/key-terms"},{"@type":"ListItem","position":3,"name":"Unit 8","item":"https://fiveable.me/ap-music-theory/unit-8"},{"@type":"ListItem","position":4,"name":"Locrian"}]}]}
```