I = Major
II = minor
III = minor
IV = Major
V = Major
VI = minor
VII = diminished
These are what are known as the Scale Line Triads. Understanding and applying this concept is absolutely essential to playing by ear (i.e., figuring out which chords are used in a song by listening to it). Here are a couple examples of scale line triads in a couple keys.
Key of C Major (the "natural key" - no sharps or flats are needed to comply with the rule of construction of a Major key, as outlined in a previous post):
I = C Major
II = D minor
III = E minor
IV = F Major
V = G Major
VI = A minor
VII = B diminished
Key of G Major (one sharp, occurring on F - so in G Major, all Fs are sharped):
I = G Major
II = A minor
III = B minor
IV = C Major
V = D Major
VI = E minor
VII = F# diminished
***SO..... before trying every chord you know when you're trying to figure out a song, pick a key, write down the Scale Line Triads in that key - I suggest using G Major to start - and when you think you hear a chord change in the song, try one of the scale line chords, Chances are very, very good that one of them will be correct!***
At this point you should take the time to write out the scale line triads in the following keys:
G Major
D Major
C Major
A Major
E Major
These are extremely common keys in various forms of American popular music and they are relatively easy to play on the guitar. That is - you won't be confronted with too many of those nasty bar chords!
In the next installment I'll reveal some tricks for determining the actual key a song is played in, common chord progressions and what to do about that pesky diminished chord (!). Until then.....
Peace & good music,
Gene