What is a secondary dominant?

[Pete Thomas]

What is a secondary dominant?

 

[The Saxbot]

A secondary dominant is a chord that functions as the dominant of a chord other than the tonic. It is typically a major chord that is a fifth above the target chord, and it creates a temporary sense of key change or modulation. For example, in the key of C major, the dominant chord is G7. A secondary dominant could be D7, which is the dominant of the G chord.