In my post about my first lesson I mentioned something about secondary dominants which was mentioned in passing by my teacher but I misunderstood. In fairness we only touched upon it for less than a minute during the session and there were many concepts whizzing by so no wonder I didn’t do it justice.
“One thing I thought I’d mention is secondary dominants. You wrote:
“There’s something called a secondary dominant, which I think is conversion of any minor chord to a dominant 7th, e.g. in key of G, conversion of Bm7 to B7 then moving to relative minor of Em.”
To clear that up, a secondary dominant is the act of approaching any chord with a dominant chord a 5th higher than it. For example, in the key of C we only get one dominant chord, the G. Take the diatonic progression C – Am – Dm – G. When we loop this progression we get the resolution from the dominant G chord back to the tonic C chord. However, we can slip in other dominant chords in front of all the other chords in the progression. A 5th above the note A is E, so before the Am chord we can approach it with an E7. In this case, E7 is a secondary dominant chord, not in the key of C, but used to create tension before resolving to the Am.
Likewise the note A is a 5th above D, so we can approach the Dm with an A7 (or any other dominant A chord). Finally the note D is a 5th above the G, so we can approach the G chord with a D7 chord.
Put it all together, and you could turn the C Am Dm G progression into C E7 Am A7 Dm D7 G. That might not sound great (I’m sat without a guitar here) due to the abundant use of minor to dominants on the same root (eg. Dm to D7), but that in principle is the use of secondary dominants. You’re probably not likely to use one before every chord in a progression as shown above – that was purely for demonstration.”
Here’s also a link to the Wikipedia reference.