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What figured bass is
Figured bass is a shorthand from the Baroque era, roughly 1600 to 1750, for writing chords above a bass line. Instead of writing out every note, the composer wrote a bass note and a few small numbers beneath it. Those numbers, the figures, told the keyboard player which intervals to play above the bass. A skilled player could read a whole accompaniment from a single bass line plus figures, improvising the details on the spot.
The system is compact because it assumes knowledge. With no figure at all, the player assumed a root position triad, the intervals of a third and a fifth above the bass. The figure 6 meant a first inversion triad, with a third and a sixth above the bass. The figure 6/4 meant a second inversion triad, with a fourth and a sixth. Seventh chords added their own figures: 7 for root position, 6/5 for first inversion, 4/3 for second inversion, and 4/2 for third inversion.
How the figures work
Each figure names intervals above the bass note, counting the bass itself as 1. So a figure of 6 on a bass note of C means: play a sixth above C, which is A, plus the assumed third, E. The result is the notes C, E and A, which is a C major chord in first inversion, with E as the lowest sounding note in the right hand but C still the bass.
Accidentals in the figures adjust single intervals. A sharp before a 6 means raise that sixth by a semitone. A flat before a 5 means lower that fifth. A natural sign cancels a sharp or flat that the key signature would otherwise impose. These small marks carry a lot of meaning, which is why reading them carefully matters.
How to use the decoder
Enter the bass note with its octave, pick a figure, and pick the key, which the decoder uses to spell the notes correctly. The decoder shows the intervals above the bass, the notes to play, and the inversion name. Try a bass of G with the figure 6/4 in C major: the decoder returns G, C and E, a C major chord in second inversion, the classic sound before a dominant chord in a cadence.
Work through a short Baroque bass line figure by figure, and you will start to recognise patterns: 6/4 to 5/3 is the cadential formula, 7 to 6 is a common suspension resolution, and chains of 6 chords are first inversion triads walking up or down a scale. Recognising those patterns is the real skill, and the decoder is a way to practise it.
Why figured bass still matters
Figured bass is not just history. It is the ancestor of modern chord symbols and of the Roman numeral analysis used in theory classes. A jazz lead sheet chord like C/E is the same idea as a 6 figure: it tells you the bass note and lets you fill in the rest. Understanding figures gives you a deeper sense of how chords and bass lines relate, which helps with arranging, improvising and analysing any music.
It also trains your ear for inversions. Many listeners hear all C major chords as the same, but a first inversion C chord sounds different from a root position one: lighter, less settled, more in motion. Figured bass forces you to notice which note is in the bass, and that attention changes how you hear.
Common mistakes
The most common mistake is reading a figure as an absolute note rather than an interval above the bass. A 6 above C is A, but a 6 above D is B: the figure moves with the bass. Another mistake is forgetting the assumed intervals: a lone 6 still includes a third, and a lone 7 still includes a third and a fifth. Finally, watch the accidentals, since a missing sharp on a 6 can turn a major chord into a minor one.
Use the decoder to check your reading, then try reading a real Baroque score. The figures will feel slow at first and then, suddenly, fast: the moment the patterns click is one of the great pleasures of music theory.
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