A Player's Guide to Chords and Harmony by Jim Aikin

figured bass, is of very little practical value today unless you happen to be a harpsichord player, but it's worth mentioning, if only because you may encounter it somewhere along the line, such as in a college-level textbook or test.

    Figure 4-8. Baroque musicians used a system called figured bass to indicate chord parts. As explained in the text, a "6" below a bass note indicates that the chord is in the first inversion, "6 4" means second inversion, and "2" indicates a 7th chord in third inversion. The bass part shown in (a) might be realized by a harpsichordist in the manner shown in (b).
    Figured bass consists of a notated bass line with numbers below certain of the notes, as shown in Figure 4-8. The system of figures, which is sensible enough, if a bit abstract, was later applied by music theorists to the system of indicating chords with Roman numerals. The same numbers that had been used in figured bass were placed to the right of the Roman numeral, thus indicating in a compact way the root of the chord (the Roman numeral), its inversion, and any additional notes contained in the voicing.
    A Roman numeral to which figured bass numbers have been attached may have a small superscript number beside it, or in some cases both superscript and subscript numbers. A chord in first inversion has a superscript "6" beside the Roman numeral. This indicates that the interval between the bass note and the root is a 6th. For instance, a 1116 chord in the key of D major would be an F# minor chord in which the A is in the bass (so that the interval between the bass and the root is a 6th). The basic idea is that in the absence of any numbering, the expected chord will have notes a 3rd and a 5th above the bass, so any deviations from this pattern will be noted.
    A chord in second inversion uses both a superscript "6" and a subscript "4" (for instance, I;), because the notes above the bass are, respectively, a 6th and a 4th above it, rather than a 5th and 3rd. Chords containing 7ths, which will be introduced in the next chapter, can also be indicated with this system. A rootposition 7th chord has a superscript "7" (for instance, IV). A 7th chord in first inversion has a superscript "6" and a subscript "5" In second inversion, a 7th chord has a superscript "4" and a subscript "3" In third inversion, a 7th chord is indicated with a superscript "4" and a subscript "2," or just a subscript "2" by itself.

    Now that you've learned about figured bass, feel free to forget about it. Once in a while you may hear a classically trained musician refer to a first-inversion 7th chord as a 6-5 chord, or to a second-inversion triad as a 6-4 chord, but other than that, the system is pretty much obsolete once you step outside the college classroom.
     

THE IMPORTANCE OF THE TONIC
    In Chapter One we talked about constructing a major scale starting on any note in the chromatic scale. I showed how key signatures derive their names from the note that's the tonic of the major scale played using that key signature. For instance, the B6 key signature (which contains two flats, one on B and the other on E) allows us to notate a B6 major scale without using any accidentals. The tonic of the key is important not just for defining the starting point of the scale, but because the triad built on the tonic chord - that is, the I chord - provides an important point of reference in any chord progression in that key.
    In the discussion that follows, I'll use the word "tonic" to refer not to the root note of the key but to the entire triad (or, potentially, a more complex chord) built on that root. The same type of usage is used for the dominant and subdominant: These words more often refer to whole chords than to scale steps.
    The tonic is a sort of anchor or resting point. Many songs - perhaps a majority - use chord progressions that both begin and end on the tonic. And when chords other than the tonic are used, they're often part of a progression that is moving either