http://www.guitartricks.com/lesson.php?input=15283&s_id=1053
A minor is the relative minor of C major and so I believe (other than the root note), all notes and chords of C major are in A minor.
Now, the song has as its first chord A major, which is not a chord in the key of C.
The song also includes, in the chorus, a D major barre chord on the 10th position. Again, D major is not a chord in the key of C (or A minor).
Have I misunderstood relative minors and their relationship to the relative major or is there another reason why these chords are in the key of A minor?
