.....I know enough that an F6 and a Dm7 share the same notes, but then I will flip through sheet music specifically a Real Book and not be able to figure out the key. Are there any books that take songs and explain the progressions more in-depth?
If you already know chord spelling you are more than half way there. Finding the key - look at where the chords are moving to within the song. That normally gives you some hints as to the key they fit into.
I chord can go anywhere in the progression it wants to, however, when you return to the I chord you resolve any tension you've built. That resolving of tension is the give-a-way you are looking for. Try and see what the I chord is doing. Does it end every verse? If so it has brought you back to the tonal center (or home) and that "home chord" will have the same name as your key. If you have
a lot of, say C major chords, in the song, C major is probably a good candidate for being the tonic chord, i.e. look for chords used a lot, that could be your tonic.
ii chord is a sub-dominant chord and it's task in life is to move to the dominant chord. Do you have a minor chord leading to a dominant seventh chord. That's a give-a-way.
iii chord is a move somewhere chord, used to start a turn-a-round, etc. The iii normally drags the vi with it.
IV chord is also a sub-dominant chord and it's task in life, like the ii, is to move to a dominant chord. The ii and the IV both having the same task and can sub for each other. Some have the IV chord going to the tonic chord, I think of this as a "second choice" it really wants to get to the dominant chord, but, since you took it to the tonic it'll not argue with you.
V chord is the dominant chord and it's task in life is to move to the tonic I chord. V7 is the climax chord and wants to move to the tonic I chord RIGHT NOW. This V-I movement is a dead give-a-way to what key is being used. Look for the dominant seventh chord. Used correctly the dominant seventh will point you to the I tonic chord. Understand songwriters throw dominant sevenths in willie nelly thinking they are adding color.....
vi chord likes to move to a sub-dominant chord. Normally the iii-vi like each other thus the iii-vi-ii-V7-I turn-a-round. I talk about relative minor chords below. That vi may be a relative minor chord, just be aware.
viidim is also a dominant chord and it's task is to move to the tonic chord, however, unlike the V or V7 the viidim likes to take a more subtle route, i.e. if you want to resolve right away use the V or V7, but, if you want to get to the I tonic through a more subtle route as in a turn-a-round the viidim is your best bet. viidim-iii-vi-ii-V7-I. As the m7b5 chord is not used a lot, when it is, it is normally telling you something. Hopefully it will be the 7th chord in the key - thus a give-a-way. At any rate see where it is going.
To find the key look at what the chords are doing - that "like to move to what" I talked about. The V-I cadence is a give-a-way. Look at the
last chord in each verse if they are the same chord, that's your key. Why? Each verse brings a thought, discusses it, reaches a conclusion, then ends this thought so the next verse can bring up another new thought. It does that by returning you back home. If each verse resolved to the same tonic chord- to end the verse - you can bet the farm that's your key.
And yes sometime you just have to play them and listen for the tonal center. Don't forget about relative minors and relative majors having the same notes and same chords - you have to see what chords are being used. C and Am. If the chords revolve around the C-F-G major chords your going to be in the key of C. If the chords revolve around the minor chords, Am-Dm-Em then the song will have a tonal center of Am. O'h yes, Harmonic and melodic minor progressions will have a major V or V7 chord
And remember songwriters do not always follow the rules, so you have to make allowances.
This all came from
www.musictheory.net. Lessons - Common chord progressions.
http://www.icce.rug.nl/~soundscapes/DATABASES/AWP/awp-notes_on.shtml takes the Beatles' songs and analyzes them. Worth a look.
Good luck.
