What's a Secondary Dominant Chord?

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In this video I’d like to explain the function of the so-called secondary dominant. Let’s start with the definition.

A secondary dominant is defined as any chord (be it a triad or a seventh) that has a dominant-like function and is built on a scale degree other than the 5th of the prevailing key. This means that all secondary dominants must be diatonic chords that have been chromatically altered to turn them into dominant 7-like chords.

So, that’s the definition and now we’ll look at some examples. By the way, the purpose of secondary dominants is to give a harmonic progression a greater sense of movement, of direction and of overall color.

Let's list all the secondary dominants available in a given key:

Here we are in the key of C major, and I have built secondary dominants on all the possible scale degrees, along with their resolutions to the respective tonics. Of the seven degrees of the C major scale, only two do not allow for a secondary dominant. These are: the 4th degree, because this would not resolve to a chord within the C major scale; and the 5th degree, because this is in fact the real dominant of the key. And by the way, the term “primary dominant” is not commonly used.

Let's listen to all five secondary dominants in the key of C major. There may be a slight lag between the sound and the visuals, due to the screen capture process.

[music plays]

Notice how each secondary dominant gives a sense of momentary modulation. This is also known as "tonicization", which means that the chord to which the secondary dominant resolves APPEARS to be a new tonic.

Now let’s look at some secondary dominants in a musical context. To do so I’ll use the first 8 bars of the 2nd movement of Beethoven's piano sonata n.8, which contains two secondary dominants. It's interesting to note, by the way, that the term “secondary dominant” was only introduced in the 1940's, so in Beethoven's time, around 1800, this harmonic device was thought of as a modulation, albeit transient.

Now as you can see from this score, I’ve reduced the music to its basic chord progression, by removing the 16th note arpeggio notes. Other than that, the chords and inversions are identical. Let's listen to this segment, and you'll see that I’ve marked the chords that act as secondary dominants.

[music plays]

Now let’s look for dominant-like chords, and determine if they are dominants or secondary dominants. To help me with this analysis, I’m using HarmonyBuilder, which will assign a different color to the root, third, fifth or seventh of each chord. I can also read the function and inversion of each chord, down here in the Nomenclature panel.

So let's move through the score...

Right here I have a dominant chord, in third inversion, as we can see from the Nomenclature panel, so this is not a secondary dominant.

Here's another dominant chord, in first inversion, which resolves to I.

Now here we get a seventh chord which has no Roman Numeral and chord symbol in the Nomenclature panel. This means this chord is not in the key of Ab major. We can find out what key this chord belongs to by using the Key menu in the Nomenclature panel, and we see that it belongs to both Eb major and Eb minor. By selecting one of these keys [Eb], we can see that it’s a Bb7 chord in 2nd inversion. Now, to be sure that it actually is a secondary dominant chord, we must check that it is in fact a chromatically altered diatonic chord. Since Bb is the 2nd degree of the Ab major scale, we can deduce that Bb7 was chromatically derived from Bbm7. We can confirm this by lowering the 3rd by a half step: the Nomenclature panel analyzes it as a Bbm7 chord, in second inversion, in the key of Ab major.

Since the root of the Bb7 resolves down a 5th to the root of the V chord, we call this secondary dominant “V7 of V”, and to indicate that this secondary dominant is in 2nd inversion, we write “V34 of V”.

Let's move on. Here we have a leading tone 7th chord, found on the VII degree of the Ab major scale, so this is not a chromatically altered chord.

Next is a dominant chord...which resolves to I in 1st inversion.

Here we have another 7th chord outside the key of Ab, as we can see from the Nomenclature panel. Note that I have added the 5th in order to analyze the chord. I can see that this chord belongs to the keys of Bb major and Bb minor, and by selecting Bbm, I see that it’s the dominant seventh of Bbm. Furthermore, by lowering the 3rd, I can see that it can be derived from a VI degree minor seventh chord, so this F7 qualifies as a secondary dominant. Furthermore, it resolves down a fifth, to the Bbm chord, which is on the 2nd degree of the Ab major scale, so we call this secondary dominant a ‘V7 of II’.

So that's the basics behind secondary dominant chords. I hope this video has helped you understand their meaning and what they sound like.

Thanks for watching.

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