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Paul McCartney has created some unusual but harmonious progressions using this musical device
PHOTO BY CHRIS PUTNAM/FUTURE PUBLISHING VIA GETTY IMAGES
Not all chord progressions stay strictly within the diatonic/chord scale convention – and that’s a good thing. Taking a little look at the theory involved here, the C major diatonic/chord scale is Cmaj-Dmin-Emin-Fmaj-Gmaj-Amin-B diminished (Bm7 b5 is also commonly used). These are often numbered sequentially using Roman numerals, so a II-V-I progression in C translates as Dm-Gmaj-Cmaj and so on. The ‘resolve’ from V to I in a chord progression is a very popular move. Let’s embellish it a bit and say the V is a V7, short for dominant 7 – namely a V chord with the b7 added. In C, G7 is the dominant (V7) that resolves to Cmaj (I).
But what if we take this move and apply it to all the other chords in the diatonic scale, and so pretend each chord in the scale (whether major or minor) is chord I and play its V7 first? In the way that G7 resolves to C, A7 would be the dominant to Dm if it were chord I (actually chord II), or B7 to Em (actually chord III). This is known as using a ‘secondary dominant’. More on this below!
Example 1