View Full Version : Keys? C Major = A Minor?

11-03-2011, 11:57 AM
Hey UU, a couple questions regrading theory -
How do you determine the key a song is in...For example, with the progression C F Am G. Is this considered to be in the key of C major or A minor because to my understanding C major and A minor scale contains the same notes. Are there any steadfast rule as to how one can determing the key of a song.


11-03-2011, 12:15 PM
C and Am scales use the same notes but songs in the two keys do not use the same primary, secondary, and tertiary chords.

When you see the C, F, and G predominant in the song it is usually in C. On the other hand, if the Am is very predominant and, especially if the phrases in the song resolve to Am instead of C, it is probably in Am. If you see the Dm quite frequently in the song, that is another clue you're probably playing in Am rather than C.

Biggest clue is where the phrases resolve, though, as most western music resolves almost all phrases to the root.

Of course, one of the lovely things about music is that for every rule there are at least a couple-dozen exceptions. :)


11-03-2011, 12:33 PM
Another way to tell if you are in Am rather than Cmajor is to look for the one note that is frequently present in Am that is never present in Cmajor: the G#.

A key feature of Western music of the last 500 years is the semi-tone distance between the 7th and 8th (second-last and last, ti and do, leading tone and tonic, etc...) notes of the scale.
In C major (and all major keys) the key signature already creates this relationship: C, D, E, F, G, A, B, C. B to C is a semi-tone.
However, in minor keys this relationship is not created by the key signature alone. An accidental (aka: sharp/flat that is added but not present in the key sig) is added to the 7th note of the scale to create this strong, "ti-do" resolution. Hence, the G# in the key of A minor rather than the G(natural) to A that is dictated by the key signature alone.

As John mentioned, there are many exceptions to this rule - particularly in folk and music of other ethnic traditions.

As he said, the easiest thing to do is to look at the first and last notes of a song and see: do they belong to the two most important chords in C major (C and G) or the two most important chords in Am (Am and E)?