Visualizing secondary dominants

Both with graphics and metaphors

In my MusicRadar column honoring Roberta Flack, I thought of a new analogy for secondary dominant chords, and I figured that I should work it into a new explainer with some new graphics. So, if you are having trouble understanding how these chords work, read on.

Secondary dominant chords solve a specific problem: how to make functional tonal harmony more interesting while still keeping things functional. The first concept you need to understand is that every major and minor key has a chord built on its fifth scale degree, the V7 chord. In Western tonal theory, these are the dominant chords, so named because they dominate the key: they create tension and suspense, which is released when you resolve to the tonic chord. The circle of fifths is a useful visualization scheme for the keys and their dominant chords.

Now let's consider the key of C major. It comprises the notes C, D, E, F, G, A, and B. You can combine these notes to form seven chords: C, Dm, E, F, G, Am, and B°. These chords sound good together in pretty much any order and any combination, but they are bland and lacking in drama. How can you introduce some more color into your C major harmony without throwing random notes and chords around?