For my music theory quiz tomorrow my professor said we need to be able to "Identify a dominant seventh chord, then tell what tonic chord it would lead to." I can identify dominant seventh chords but I'm not sure what he means by "tell what tonic chord it would lead to". Can anyone help me with this? Thanks.
The dominant chord of a scale can be used to 'drive' the harmony toward the tonic. We say that the dominant's function is to resolve to the tonic. The dominant chord doesn't have to be used this way, for example it can be followed by the sub-mediant (chord vi) to make an interrupted cadence. But the relationship between the tonic and the dominant is very important indeed.
We know that for a specific key, there will be one tonic and one dominant based on the notes of the 1st and 5th degrees of the scale respectively.
So your it sounds like your professor is asking you to determine what the key is based on the dominant 7th chord you have been given.
How do you do this?
Here's an example: take a G7 chord. You know that the dominant of a key falls on the 5th degree of the scale, so you just need to find for which scale G is degree 5. Start with 5 at G and count down until you reach 1 and you get... C. So G7 is the dominant seventh chord of C major.
Note that the dominant seventh chord can be built from notes that occur naturally in a scale (e.g. G-B-D-F in G7 are all found in the C major scale).