Borrowed Chords and Secondary Dominants: The Secret Ingredients of Chord Progressions

In the last post we discussed the concept of chord progressions and how the individual chords in the sequence are related to each other. Today I want to talk about chords in a progression that fall outside the standard key signature of the piece, particularly borrowed chords and secondary dominants.

A borrowed chord, is a chord in a progression that is taken from the parallel key (the minor or major scale with the same tonic). An example of a parallel key would be (Cmin) in relation to (Cmaj). Both scales in their respective keys start with (C), hence (C) is the tonic of both keys, making them parallel in structure. A piece of music using borrowed chords uses this parallel structure to provide variety and a different "feel" to the song. For example, the song "Happy Together" by the Turtles uses borrowed chords to change the song from major to minor between the chorus and the verse. Listen to the song below and see if you can hear the spots in which chords are taken out of the original key:

The next concept I want to talk about is that of secondary dominants. As we know from a previous post, the dominant of key is the fifth triad above the tonic. So if we are in the key of C major, the dominant triad is G major. As discussed in last weeks post there is a very strong relationship between the dominant and the tonic, so much so that many cadences (chord progressions that bring about the end of a musical phrase) are centered around them. So we know what the "dominant" is, but what does the "secondary"part mean? Let's look at an example of a chord progression that uses a secondary dominant to see if we can find out. 

I apologize for the poor quality of the picture, but this is a perfect example of a secondary dominant chord used in the key of C Major. Here we see that the piece starts on the tonic (C), then goes to the subdominant or the Four Chord (F). After the four chord however, something happens that gives us a D Major chord before going to the dominant (G) and resolving with the tonic (C). What is going on? 

This is what is known as a secondary dominant. As defined it is the use of the dominant "of the dominant" of the set key. So if the set key in this case is (C major) the dominant is (G major) and the dominant of that is (D Major). If you have a piano this relationship can be seen my going up two fifth intervals from C. (C --> G --> D). In the key of G major the dominant is D Major (because in G major the F is sharp) and this gives us a chord that is taken outside of its original key but is related to the dominant of the key the piece is played in. 

Secondary dominants can be used in different ways throughout music, and it does not always have to be the dominant of the dominant. You can have a secondary dominant that is based off the (ii) chord in a piece, such as what is used in "Tears of Heaven" by Eric Clapton, or one that is taken from the (Vi) chord as in "Yesterday" by the Beatles. Here is an example of a chord progression that implements secondary dominance:   

In a couple days I will post a follow-up post that has a couple more examples of borrowed chords and secondary dominants, as this was meant to be an introduction to the concept. If you have any comments or questions then please post below, but other than that thank you for reading!

-Sincerely, ZS