21.10Secondary dominants

Now make destinations stronger.

Original:

C | Am | Dm | G7 | C

Insert:

E7 → Am

and:

A7 → Dm

Result:

C | E7 Am | A7 Dm | G7 | C

Or with sevenths:

Cmaj7 | E7 Am7 | A7 Dm7 | G7 | Cmaj7

Now the harmony has much more direction.