In AP Music Theory, Arabic numerals (also called figures) are the numbers in figured bass that tell you which intervals to build above a given bass note, which is how chord inversions get labeled (6 for first inversion, 6/4 for second inversion, with root position's 5/3 usually left blank).
Outside of music, Arabic numerals are just the digits 0-9. In AP Music Theory, they have a very specific job. They are the small numbers attached to figured bass and Roman numeral analysis that tell you which intervals appear above the bass note. A 6 means there's a pitch a sixth above the bass. A 6/4 means a sixth and a fourth above the bass. No numbers at all means the default, a fifth and a third above the bass (root position).
This is the system the CED describes in PIT-2.A.2 and PIT-2.B.1. Because the figures define which chord members sit above the bass, they automatically tell you the inversion. Root position gets the implied 5/3, first inversion (third in the bass) gets 6, and second inversion (fifth in the bass) gets 6/4. Figures can also carry accidentals. A slash or plus sign through a figure raises that pitch a half step, and an accidental written alone (with no numeral) applies to the third above the bass. Octave equivalents count, so a "sixth above the bass" can show up an octave higher in an actual voicing. For the full system, head to the [3.3 study guide on Chord Inversions and Figures](topic 3.3).
Arabic numerals live in Topic 3.3 (Chord Inversions and Figures) in Unit 3: Music Fundamentals III. They directly support two learning objectives. AP Music Theory 3.3.A asks you to identify chords using letters plus Roman and Arabic numerals that show the root's scale degree, the quality, and the bass note. AP Music Theory 3.3.B asks you to read a figured bass and translate it into Roman numerals, which only works if you can decode the figures. Here's the intuitive version. Roman numerals answer "which chord is it?" and Arabic numerals answer "how is it stacked?" You need both halves to fully label a harmony, and that combined label (like V6/4 or ii6) is the language of every harmonic analysis, dictation, and part-writing task from Unit 3 onward.
Keep studying AP Music Theory Unit 3
Visual cheatsheet
view galleryFigured Bass (Unit 3)
Figured bass IS Arabic numerals in action. It's a Baroque shorthand where a bass line plus figures tells a performer (or you, on the exam) exactly which chords to realize above each bass note.
Roman Numerals (Unit 3)
Roman and Arabic numerals work as a team. The Roman numeral names the chord by its scale-degree root and quality, and the Arabic numerals beside it name the inversion. V6/4 only makes sense because both systems are doing their separate jobs.
Chord Inversion (Unit 3)
Inversions are the concept; Arabic numerals are the labels. When the third of the chord is in the bass, the interval pattern above it is 6/3, so we write 6. When the fifth is in the bass, the pattern is 6/4. The figures literally describe what's happening above the bass.
Arabic numerals show up everywhere chords get labeled. Multiple-choice questions ask things like what a bass note with 6 and 4 below it indicates, or which intervals are implied when a bass note has no figures at all (answer: a fifth and a third, root position). On the free-response side, the composition FRQ (Question 7 on the 2023 and 2024 exams) requires you to write a bass line and then label each chord with both Roman AND Arabic numerals following eighteenth-century voice-leading procedures. Harmonic dictation FRQs (like 2024 Question 4 and the 2017 harmonic progression question) also expect inversion figures in your Roman numeral answers. So you can't just hear that a chord is V; you have to notice the bass note and write V6 or V6/4 when the dominant isn't in root position. Sloppy or missing figures cost real points.
Roman numerals (I, ii, V, vii°) identify the chord itself, meaning its root's scale degree and its quality. Arabic numerals (6, 6/4, 7, 6/5) identify the inversion by listing intervals above the bass. A common mix-up is thinking the Arabic numeral names a chord member ("6 means the sixth scale degree"). It doesn't. The 6 in ii6 means there is a pitch a sixth above the bass, which tells you the chord's third is in the bass. One system asks "what chord?", the other asks "what's on the bottom?"
Arabic numerals in figured bass denote pitches at specific intervals above the bass note, and octave equivalents of those pitches are acceptable.
Root position is the unfigured default (implied 5/3), first inversion is labeled 6, and second inversion is labeled 6/4.
A slash or plus sign through a figure raises that pitch a half step, and an accidental standing alone applies to the third above the bass.
Roman numerals name the chord's root and quality, while Arabic numerals name the inversion; AP analysis labels like V6/5 combine both.
On the composition FRQ you must write both Roman and Arabic numerals below your bass line, so missing inversion figures lose points even if the chord choice is right.
They're the figures in figured bass and harmonic analysis that show intervals above the bass note. A 6 means first inversion (sixth above the bass), 6/4 means second inversion, and no figure means root position with an implied 5/3.
Roman numerals identify which chord it is (root scale degree and quality, like V or ii), while Arabic numerals identify the inversion (which chord member is in the bass). You combine them in labels like V6 or ii6/5.
No. An unfigured bass note implies the default intervals of a fifth and a third above the bass, meaning a root-position triad. The 5/3 is simply left off by convention.
It means there's a pitch a sixth above the bass and another a fourth above the bass, which puts the chord's fifth in the bass. That's a second-inversion triad, like writing I6/4 when the tonic chord has its fifth on the bottom.
Yes. The composition FRQ (Question 7) explicitly asks for Roman and Arabic numerals below your bass line, and harmonic dictation answers need inversion figures too. Writing V when the chord is actually V6/4 is an incomplete answer.
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