In class we have been talking about secondary dominants, where you temporarily treat a chord as a new key center before returning to the main key. In a modulation, you move to a new key center and stay there (for a while, anyway). Modulations were a common songwriting technique in pre-rock popular music, and a somewhat less common one in the rock era. They have become increasingly rare in the Anglo-American pop mainstream, though they are still a feature of game and film scores.








