Figured bass is a shorthand method of indicating chords. The lowest voice is written out, and numbers are added above it that indicate the intervals used to form the chord. Thus the bass note is written, and by constructing the intervals given above it, the chord can be spelled out.
Figured Bass is combined with Roman Numerals to provide a shorthand method of indicating chords and harmonic rhythm. For example, I vi I64 V7 I indicates a chord progression of five chords. The Roman numerals number symbols that use letters of the alphabet, I II III IV V VI VII for 1 2 3 4 5 6 7 show the function of the chords within the key. The figured bass, 64, indicates the second inversion, and the 7 indicates that the V chord has an added 7th. A skilled musician can look this and imagine the sound of the chord progression and also play it in any key. In addition, it can be played with different chord spacings or voicings. There are many versions of how this might be played. Other factors such as rhythm, tempo the rate or speed of the musical pulse, style, register, and instrumentation are also variables. However, this shorthand reveals the harmony and harmonic rhythm.
How to read Figured Bass with Roman Numerals
A Roman numeral by itself indicates a root position triad a three note chord consisting of a 3rd and 5th above a root: Major, minor, diminished, Augmented, see Chord Construction. The lowest note has a 5th and a 3rd above it.
C Major root position
A Roman numeral followed by 6 indicates a 1st inversion triad. The bass note has a 6th and a 3rd above it. This example shows the C Major I chord in open and closed voicing in 1st inversion:
C Major 1st inversion
A Roman numeral followed by 64 indicates a 2nd inversion triad.
C Major 2nd inversion
A Roman numeral followed by 7 indicates a root position seventh chord.
G7 root position
A Roman numeral followed by 65 indicates a 1st inversion seventh chord.
G7 1st inversion
A Roman numeral followed by 43 indicates a 2nd inversion seventh chord.
G7 2nd inversion
A Roman numeral followed by 42 indicates a third inversion seventh chord.
G7 3rd inversion
see also: Roman Numeral Analysis, Open Voicing Chords, Scale-tone chords, Staff Roman Numeral Chords