What is "Figured Bass"? I, IV, V7, etc.

Figured bass is a type of notation that uses numbers to denote certain intervals or chords. It was used extensively during the classical period and is still taught in college music theory courses today.

 It can be viewed as a sort of musical shorthand; only the bass note is shown on the staff, and the numbers written underneath indicate the general idea of what should be played. Figured bass is very similar to Baroque era's basso continuo, a type of minimal notation given to accompanists. The accompanists working with the basso continuo or figured bass knew the basic structure of the song but had to rely on improvisation to complete the entire piece. Improvisation is important here because figured bass only indicates the song's harmony; the rest is decided by each musician, depending on the style and tone of the music and the other instruments involved.

The figured bass notation is based solely on the bass line. The bass note is shown on the staff, as usual, but underneath are a series of numbers. These numbers in figured bass notation denote the intervals with which the chord is to be played; any accidentals are written next to the numbers. For instance, if an F is shown on the staff with a four and six underneath it, the figured bass notation is telling the musician to play an F chord with notes a fourth and sixth above the F. And if that four, for example, is shown with a flat sign, the figured bass is telling the musician to play the fourth a half step down.

If the chord contains a third or a fifth, however, these numbers are often omitted from the figured bass. A third and fifth with any bass note creates a triad; the sheer commonality of triads led those using figured bass to get rid of the numbers and simply assume their presence. Likewise, if only one number is present underneath the bass note, figured bass assumes the missing note to be a third.

Even the bass notes themselves are sometimes left out of the figured bass notation to keep the shorthand truly short. If a bass note repeats itself for several bars, only the first instance of the note will be shown in the figured bass; after that, the only thing to denote the chord will be the series of numbers. Until it changes, the bass note here is completely assumed.