Do you pick music based on your mood, or to change your mood?

When you listen to music, do you tend to listen to music that matches how you already feel, or try to alter how you feel with music? Does it depend on the situation or your emotions to begin with? Do emotions have little or nothing to do with how you select which music to listen to?

My first inclination is to reach for music that matches my mood. Hence, listening to Primus and Soundgarden when I was feeling all twisted up yesterday. I also can alter my mood with music, sometimes. Afro Celt Sound System is just fantastic for that and has saved my hide a number of times.