---
title: "Contrary Motion — AP Music Theory Definition & Exam Guide"
description: "Contrary motion is when two voices move in opposite directions. It's the gold standard for voice independence in AP Music Theory part writing and bass-line FRQs."
canonical: "https://fiveable.me/ap-music-theory/key-terms/contrary-motion"
type: "key-term"
subject: "AP Music Theory"
unit: "Unit 4"
---

# Contrary Motion — AP Music Theory Definition & Exam Guide

## Definition

Contrary motion is when two voices move in opposite directions (one ascends while the other descends). In AP Music Theory, it's one of the four types of linear motion between voices (PIT-4.A.2) and the most reliable way to create voice independence and avoid parallel fifths and octaves in 18th-century part writing.

## What It Is

Contrary motion happens when two [musical lines](/ap-music-theory/unit-4/satb-voice-leading/study-guide/c71tSuvM22gVBJGNiw1V "fv-autolink") move in opposite directions at the same time. The [soprano](/ap-music-theory/key-terms/soprano "fv-autolink") goes up, the bass goes down (or the reverse). That's it. The CED lists it as one of four ways two voices can move relative to each other (PIT-4.A.2): parallel, similar, oblique, and contrary.

Why does the exam care so much about it? Because 18th-century voice leading is built on a tension between two goals. Chords need to lock together vertically, but each voice should still sound like its own independent [melody](/ap-music-theory/unit-2/melodic-transposition/study-guide/37yjbA6PqIr71IzgG9iY "fv-autolink") (PIT-4.A.1). Contrary motion is the strongest tool for that independence. When the outer voices move in opposite directions, they literally cannot form parallel fifths or octaves with each other, which is why it's the safest default move when you're composing a bass line under a given soprano. Think of it as the anti-parallel-fifths insurance policy.

## Why It Matters

Contrary motion lives at the heart of **[Unit 4](/ap-music-theory/unit-4 "fv-autolink") (Harmony and Voice Leading I)**, especially Topic 4.1. Learning objective [AP Music Theory](/ap-music-theory "fv-autolink") 4.1.A asks you to identify and apply 18th-century voice-leading procedures through score analysis, error detection, writing exercises, and listening, and recognizing the four motion types is step one of all of that. It matters even more for AP Music Theory 4.1.B and 4.1.E, where you compose a bass line under a given soprano. The CED says bass lines should balance upward and downward motion (PIT-3.D.1), and writing in contrary motion against the soprano is the easiest way to hit that target while dodging parallelism errors.

It also threads into **Unit 5**. Predominant chords (IV, ii, ii⁷) moving to V are a classic spot where contrary motion between the bass and upper voices keeps the progression clean (Topics 5.1 and 5.3). And the [Phrygian half cadence](/ap-music-theory/key-terms/phrygian-half-cadence "fv-autolink") (iv⁶–V in minor, PIT-2.I.3) is practically a poster child for contrary motion, with the bass descending by half step while an upper voice ascends to the dominant.

## Connections

### [Parallel motion (Unit 4)](/ap-music-theory/key-terms/parallel-motion)

[Parallel motion](/ap-music-theory/key-terms/parallel-motion "fv-autolink") is contrary motion's opposite. Both voices move the same direction by the same interval. Parallel thirds and sixths are fine, but parallel fifths and octaves are the cardinal sins of 18th-century style, and contrary motion is your main escape route from them.

### Voice leading (Units 4-5)

[Voice leading](/ap-music-theory/unit-5/cadential-64-chords/study-guide/Fmolx6ik4nmpMVO4inHe "fv-autolink") is the whole system of how individual parts move from chord to chord (PIT-4.A.1), and contrary motion is one of its core tools. The style wants linear smoothness plus voice independence, and opposite-direction movement delivers the independence half of that equation.

### Cadences and Predominant Function (Unit 5)

The Phrygian half cadence (iv⁶–V in minor) is the textbook cadence built on contrary motion. The bass falls by half step to the dominant while an upper voice rises to it, and that opposite-direction squeeze is what gives the cadence its distinctive sound (PIT-2.I.3).

### Texture and Texture Types (Unit 2)

Polyphony is defined by multiple independent melodic lines, and contrary motion is one of the clearest audible signals of that independence. If two lines constantly move in opposite directions, your ear hears them as separate melodies rather than one thickened line.

## On the AP Exam

Contrary motion shows up most directly in the part-writing FRQs. The 2025 exam's SAQ Q7 asked you to complete a bass line under a given melody following 18th-century voice-leading procedures, then label the harmony with Roman and Arabic numerals. That task rewards contrary motion twice over. It keeps your outer voices free of parallel fifths and octaves, and it satisfies the CED's call for a bass line that balances upward and downward motion. Multiple-choice questions test it more analytically, asking what effect contrary motion between outer voices has on a progression, or how voice leading into a predominant chord avoids parallelism. Error-detection questions (AP Music Theory 4.1.A) often hinge on spotting where a passage should have used contrary motion but created forbidden parallels instead. Bottom line on exam day: when your soprano steps up, try stepping the bass down first.

## Contrary motion vs Similar motion

Both contrary and similar motion involve two voices changing pitch at the same time, so students mix them up. In similar motion, both voices move the SAME direction but by different intervals. In contrary motion, they move OPPOSITE directions. The difference matters because similar motion can still produce problems (like hidden fifths and octaves between outer voices), while contrary motion between two voices can never create parallel fifths or octaves between them. Also don't confuse contrary with oblique motion, where one voice holds still while the other moves.

## Key Takeaways

- Contrary motion means two voices move in opposite directions, and it's one of the four motion types in the CED alongside parallel, similar, and oblique motion (PIT-4.A.2).
- Two voices moving in contrary motion cannot create parallel fifths or octaves with each other, which makes it the safest motion type in 18th-century part writing.
- When composing a bass line under a given soprano on the FRQ, defaulting to contrary motion helps you balance upward and downward movement, which the CED explicitly requires (PIT-3.D.1).
- The Phrygian half cadence (iv⁶–V in minor) is built on contrary motion, with the bass descending by half step while an upper voice ascends to the dominant.
- Contrary motion creates voice independence, which is the defining feature of polyphonic texture in Unit 2 and a core goal of voice leading in Units 4 and 5.

## FAQs

### What is contrary motion in music theory?

Contrary motion is when two voices or melodic lines move in opposite directions at the same time, like the soprano stepping up while the bass steps down. It's one of the four motion types (parallel, similar, oblique, contrary) tested in AP Music Theory Unit 4.

### Is contrary motion always required in AP part writing?

No. Parallel thirds and sixths, similar motion, and oblique motion are all perfectly legal in 18th-century style. Contrary motion is just the safest choice because it can never produce parallel fifths or octaves between the two voices involved, so it's a smart default for outer voices on the bass-line FRQ.

### How is contrary motion different from oblique motion?

In contrary motion, both voices move, just in opposite directions. In oblique motion, one voice stays on the same pitch while the other moves. Both create voice independence, but the exam expects you to label them as distinct motion types.

### Why does contrary motion prevent parallel fifths and octaves?

Parallel fifths and octaves require both voices to move in the same direction while keeping the same interval. If the voices move in opposite directions, the interval between them has to change, so consecutive perfect fifths or octaves are impossible between those two voices.

### Where does contrary motion show up on the AP Music Theory exam?

Mainly in the part-writing FRQs, like the 2025 SAQ that asked for a bass line under a given melody following 18th-century procedures, plus error-detection and analysis questions under learning objective AP Music Theory 4.1.A. It also helps explain the voice leading of the Phrygian half cadence in Unit 5.

## Related Study Guides

- [4.1 Harmony and Voice Leading I](/ap-music-theory/unit-4/harmony-voice-leading-i/study-guide/0m8OiGeqjebWSd6bMZ0W)
- [Unit 2 Overview: Music Fundamentals II (Minor Scales and Key Signatures, Melody, Timbre, and Texture)](/ap-music-theory/unit-2/review/study-guide/9dk9TL5hgjMd1jPZMwqv)
- [2.11 Texture and Texture Types](/ap-music-theory/unit-2/texture-texture-types/study-guide/A6RcZJWtcKHnp2uenmmJ)
- [5.3 Predominant Seventh Chords](/ap-music-theory/unit-5/predominant-seventh-chords/study-guide/HtMsIFkpBnOwGkqOvqlQ)
- [5.5 Cadences and Predominant Function](/ap-music-theory/unit-5/cadences-predominant-function/study-guide/INNHEx3QCfTJPy2yXPqC)
- [Unit 5 Overview: Harmony and Voice Leading II (Chord Progressions and Predominant Function)](/ap-music-theory/unit-5/review/study-guide/MzVcs3ZCCoLXj93MHX53)
- [5.1 Adding Predominant Function IV (iv) and ii (ii0) to a Melodic Phrase](/ap-music-theory/unit-5/adding-predominant-function-iv-iv-ii-ii0-melodic-phrase/study-guide/k9mbg8yvU736povWYW7W)

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