Now, let's embellish this C major chord progression using secondary dominants:

First, let's prepare the IV chord by preceding it with its dominant. The IV chord is F major, and C7 is its dominant chord:

We write V/IV to indicate a secondary dominant chord of the IV degree. These chords are referred to as V of IV, V of V, and so on.

Now, let's do the same with the V-degree chord. The dominant chord of G is D7:

We added harmonic interest to the original chord progression by using these secondary dominant chords.

The opening measures of Beethoven's First Symphony are an excellent example of the use of secondary dominants. Note the use of the secondary dominants of the IV and V degrees:

Below, we list all the secondary dominant chords for each degree in the key of C major:

Diminished seventh chords have a similar harmonic function. They can also be used as secondary diminished seventh chords. Below, we show all the diminished seventh chords in C major: