Oblique motion is one of the four types of relative motion between two voices in 18th-century voice leading (AP Music Theory 4.1.A), in which one voice stays on the same pitch while the other voice moves up or down.
Oblique motion describes what happens between two voices when one of them holds (or repeats) its pitch while the other one moves by step or leap. Picture a soprano climbing from C to D to E while the bass just sits on G. The bass is the anchor, the soprano is the mover, and the relationship between them is oblique.
In the CED, oblique motion is one of the four ways linear movement can happen between two voices (PIT-4.A.2), alongside parallel, similar, and contrary motion. These four labels are the vocabulary of voice leading, which is the whole subject of Topic 4.1. Voice leading in the common-practice style is supposed to create smooth lines and independent voices, and oblique motion is a built-in independence machine. One voice literally refuses to follow the other. It also keeps you out of trouble, because the classic part-writing errors (parallel fifths and parallel octaves) require both voices to move. If one voice is standing still, parallels are impossible between that pair.
Oblique motion lives in Unit 4, Topic 4.1 (Harmony and Voice Leading I) and directly supports learning objective 4.1.A, which asks you to identify and apply 18th-century voice-leading procedures through score analysis, error detection, writing exercises, and contextual listening. You can't do any of those tasks without instantly recognizing all four motion types. It also connects back to Unit 2, Topic 2.11 (Texture and Texture Types) under 2.11.A, because a sustained note against a moving line is a textural event too. A drone under a melody is oblique motion stretched across a whole passage. When you compose a bass line under a given soprano (4.1.B and 4.1.E), oblique motion shows up naturally whenever the bass repeats a note while the soprano keeps moving, and the CED explicitly allows that kind of repetition as long as the harmonic progression stays plausible.
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Visual cheatsheet
view galleryContrary Motion (Unit 4)
Contrary and oblique motion are the two independence-builders in voice leading. Contrary motion gets independence by having both voices move in opposite directions, while oblique motion gets it by having one voice not move at all. The exam treats them as the two 'good citizen' motions of 18th-century style.
Parallel Motion (Unit 4)
Parallel motion is the opposite end of the spectrum, since both voices move the same direction by the same interval. Here's the practical payoff for part writing: parallel fifths and octaves require two moving voices, so any voice pair in oblique motion is automatically safe from that error.
Voice Leading (Unit 4)
Oblique motion is one of the four building blocks of voice leading under PIT-4.A.1, which says voices should achieve linear smoothness and independence. Holding a common tone between two chords in one voice while another voice moves is textbook smooth voice leading, and it's oblique motion by definition.
Texture and Texture Types (Unit 2)
Topic 2.11 looks at how lines combine into an overall sound. A sustained pitch (like a drone or pedal tone) underneath an active melody is oblique motion operating at the texture level, so the same listening skill earns you points in both Unit 2 and Unit 4 questions.
Oblique motion is most often tested as a quick identification task. A typical multiple-choice stem shows or describes two voices and asks which motion type connects them, with parallel, similar, oblique, and contrary as the four answer choices. The giveaway for oblique is always the same: one voice's pitch doesn't change. The concept also feeds the part-writing free-response tasks. When you compose a bass line under a given soprano (4.1.B, 4.1.E) or do error detection (4.1.A), you're constantly classifying motion between voice pairs, and recognizing oblique motion fast tells you that pair can't contain parallel fifths or octaves. In contextual listening and outer-voice dictation (4.1.D), hearing one line hold steady while the other moves is a clue about which voice is carrying the melodic activity.
Both terms sound like 'the voices aren't cooperating,' so they get swapped constantly. The difference is how many voices actually move. In contrary motion, BOTH voices move, just in opposite directions (one up, one down). In oblique motion, only ONE voice moves while the other stays planted on its pitch. Quick test: count the moving voices. Two movers in opposite directions is contrary; one mover plus one anchor is oblique.
Oblique motion means one voice stays on the same pitch while the other voice moves up or down.
It is one of the four motion types in the CED (parallel, similar, oblique, contrary) under learning objective 4.1.A and PIT-4.A.2.
Oblique motion can never create parallel fifths or octaves between two voices, because parallels require both voices to move.
Along with contrary motion, oblique motion helps create the independence of voices that 18th-century voice leading demands.
A drone or pedal tone under a moving melody is oblique motion at the texture level, connecting Unit 4 voice leading back to Topic 2.11.
Oblique motion is the relationship between two voices where one voice holds or repeats its pitch while the other voice moves. It's one of the four motion types (with parallel, similar, and contrary) covered in Topic 4.1 on 18th-century voice leading.
No. In contrary motion both voices move in opposite directions, but in oblique motion only one voice moves while the other stays on the same pitch. Count the moving voices: two means contrary, one means oblique.
No. Parallel fifths and octaves require both voices to move, so a voice pair in oblique motion is automatically safe from that error. That makes oblique motion a reliable tool in part-writing FRQs.
Parallel motion (both voices move the same direction by the same interval), similar motion (same direction, different intervals), oblique motion (one voice holds while the other moves), and contrary motion (voices move in opposite directions). All four come from PIT-4.A.2 in the CED.
Yes, completely. It's one of the standard motion types and actually helps achieve the independence of voices the style requires. Keeping a common tone in one voice while another moves is a classic smooth voice-leading move.
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