Augmented second in AP Music Theory

An augmented second is an interval spanning two letter names that is one chromatic semitone larger than a major second (e.g., A♭ up to B). It sounds identical to a minor third but is spelled differently, and it's treated as a melodic error in traditional part-writing.

What is Augmented second?

An augmented second is what you get when you take a major second and stretch it by one more chromatic semitone without changing the letter names. A♭ up to B is the classic example. Count it out: A♭ to B♭ is a major second, so A♭ to B natural is augmented. Per the CED (PIT-1.L.1), every interval gets a size (second, third, fifth) and a quality (major, minor, perfect, diminished, augmented), and spelling determines both. That's why A♭–B is an augmented second while the identical-sounding G♯–B is a minor third. Same sound, different spelling, different name. They're enharmonic equivalents.

The augmented second shows up naturally in one very specific place you need to know cold: the harmonic minor scale, between scale degree 6 and the raised leading tone (degree 7). In C harmonic minor, that's A♭ up to B. This gap is exactly why the melodic minor scale exists. Raising scale degree 6 on the way up smooths out the awkward leap. Later in the course, that same logic becomes a part-writing rule, because a melodic augmented second in a voice part counts as a voice-leading error.

Why Augmented second matters in AP® Music Theory

This term lives in Topic 2.5: Interval Size and Quality (Unit 2) and supports learning objective 2.5.A, which asks you to describe the size and quality of intervals in both performed and notated music. The augmented second is the interval that forces you to actually count letter names and semitones instead of trusting your ear, because your ear will tell you 'minor third' every time. It also explains the structure of the harmonic and melodic minor scales, which are the other big content block in Unit 2. So one term ties together interval quality, enharmonic spelling, and why minor scales come in three flavors.

How Augmented second connects across the course

Enharmonic equivalent (Unit 2)

The augmented second and the minor third are the textbook enharmonic pair, just like the augmented fourth and diminished fifth named in the CED. A♭–B and G♯–B are the same three semitones, but the letter names decide which one you write. On the exam, the spelling on the page always wins over what your ear says.

Minor scales and key signatures (Unit 2)

The harmonic minor scale builds an augmented second right into itself, between scale degree 6 and the raised seventh. The melodic minor scale raises degree 6 in its ascending form specifically to erase that gap. If a question asks why melodic minor exists, the augmented second is the answer.

Part-writing (Units 5-6)

In four-part voice leading, a melodic augmented second in any voice is a graded error. This usually traps you in minor keys, when a voice moves from scale degree 6 up to the raised leading tone. Knowing the interval in Unit 2 is what lets you spot and avoid the error later.

Chromaticism (Units 2+)

Augmented and diminished intervals are where chromatic alterations show up in interval naming. Raising or lowering a note by a chromatic semitone (same letter, new accidental) changes quality but not size, which is exactly how a major second becomes an augmented second.

Is Augmented second on the AP® Music Theory exam?

Expect the augmented second in multiple-choice interval identification, both notated and aural. A common stem asks for the interval between scale degree 6 and the leading tone in a harmonic minor key (in C harmonic minor, A♭ to B is an augmented second). Another favorite tests chromatic alteration logic, like what happens when you raise or lower one note of a given interval by a chromatic semitone, or asks which interval is the enharmonic equivalent of an augmented second (minor third, spelled with different letter names). Aurally, you can't distinguish it from a minor third by sound alone, so notation-based questions hinge entirely on letter-name counting. In the part-writing FRQs (Questions 5 and 6 on the free-response section), writing a melodic augmented second in a voice part, typically ♭6 up to raised 7 in minor, costs you points as a voice-leading error.

Augmented second vs Minor third

They sound exactly the same (three semitones) but are spelled differently. An augmented second spans two letter names (A♭ to B), while a minor third spans three (A♭ to C♭, or G♯ to B). Interval size comes from counting letters, not semitones, so the written spelling is the only way to tell them apart. In context they also behave differently. A minor third is a normal, stable melodic interval, while an augmented second is flagged as awkward and avoided in traditional voice leading.

Key things to remember about Augmented second

• An augmented second is one chromatic semitone larger than a major second and spans two letter names, like A♭ up to B.

• It is the enharmonic equivalent of a minor third, so it sounds identical but is spelled with different letter names.

• The harmonic minor scale contains a built-in augmented second between scale degree 6 and the raised leading tone, and the melodic minor scale raises degree 6 to avoid it.

• Interval size is determined by counting letter names, not semitones, so spelling decides whether three semitones is an augmented second or a minor third.

• In part-writing, a melodic augmented second in a voice part is a voice-leading error, most often triggered in minor keys when moving from ♭6 to the raised 7.

Frequently asked questions about Augmented second

What is an augmented second in music theory?

It's an interval spanning two letter names that is one chromatic semitone larger than a major second, such as A♭ up to B (three semitones total). It appears naturally in the harmonic minor scale between scale degrees 6 and 7.

Is an augmented second the same as a minor third?

No, even though they sound identical. Both contain three semitones, but an augmented second spans two letter names (A♭–B) while a minor third spans three (G♯–B). They are enharmonic equivalents, and the spelling on the page determines which one it is.

Why is the augmented second avoided in part-writing?

Traditional voice leading treats it as an awkward melodic leap, so writing one in a voice part counts as an error on the part-writing FRQs. The most common trap is moving from scale degree ♭6 up to the raised leading tone in a minor key.

Where does the augmented second occur in the harmonic minor scale?

Between scale degree 6 and the raised scale degree 7. In C harmonic minor, that's A♭ up to B natural. This gap is the whole reason the ascending melodic minor scale raises degree 6 as well.

Can you hear the difference between an augmented second and a minor third?

Not in isolation. They're the same number of semitones, so they sound identical out of context. On aural questions you'll typically hear it labeled by sound as a minor third, while notated questions require you to count letter names to get the correct spelling-based answer.