Switching one chord for another – done most easily when both chords belong to the same class.
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The Eagles’ first hit single, “Take It Easy“, nicely demonstrates how replacing one chord with another can subtly change the character of a chord progression. The song is in the key of G major, and the chord progression of the opening line is: G D C. Harmonically speaking, that’s a very strong way to start: tonic chord (I) followed by dominant chord (V), followed by subdominant (IV), before returning to the I-chord for the second line.
After the instrumental break that follows the second verse, they swap the IV-chord for a ii-chord, changing the progression to: G D Am. (In fact, the third chord is Am7, the 7th being created by the melody note G.)
The reason that a IV-chord can be replaced with a ii-chord so easily is that both chords fulfill a similar subdominant function. They are both considered to be members of a chord class called subdominant. The two chords have two notes in common with each other:
Two chords that belong to the same chord class can usually be interchanged, as long as the melody note that you’re harmonizing belongs to both chords. In the case of “Take It Easy”, a 7th was added to the ii-chord in order to make the melody note fit. Adding a 7th, or indeed any extra pitch, to a chord does not usually change its function.
There are a few tips to consider when substituting one chord for another.
First, both chords should be members of the same chord class. There are three main classes of chords: Tonic, subdominant and dominant, named after their most common chord members:
Second, while it’s definitely worth experimenting with your chord progressions to familiarize yourself with the way the character of your music changes with each substitution, don’t get too heavy-handed with doing chord substitutions throughout a song. Particularly in the pop music genres, audiences like a good deal of predictability. Switching chords throughout a song may create an unsettled feeling in the listener.
Third, it’s possible to switch chords from different chord classes. “Help Me Rhonda”, written by Brian Wilson, Mike Love, recorded by the Beach Boys, demonstrates this. The second chord is a dominant chord (V7, the 7th being created by the melody note). The 7th of a dominant chord is a note that also exists in the IV-chord. So when Johnny Rivers recorded his version of “Help Me Rhonda”, he switched the dominant chord for a subdominant one.
That kind of switching between chord classes is often difficult to do, and so be sure that you’ve given it a good listen before you go with it.
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