Okay so im mainly a guitar guy that dabbles with keyboards too. I have a somewhat solid base in musical theory, i know the seven modes of the scales + harmonic minor, i know the formula behind the scales, meaning they aren't just notes to me but a progression of whole and half tones, like a major chord goes from root, up one whole tone, up another whole, then a half, then a whole, then a whole, another whole, then up another half back to the root. I know that songs are made by building chords out of the tones of the scales. C major (C D E F G A B C) uses the chord C major because the I, III, and V tones are all from the C major scale, D minor because starting on D as the I makes F the III and A the V, but the D major scale goes D E F#, so in the key of C, D has to be minor. So on and so forth, the pattern of chords is I ii iii IV V(7) vi vii(dim). I understand that by this formula songs are supposed to only have 3 major chords at most. But i know that this is not the case.
My problem comes in where there are songs that somehow have 4 and more major chords during one part of a song. I can tell they're not key changes, but i'm just confused as to why it works musically for songs to have more than three major chords. Also i am confused as to why it works musically when you switch to the minor of a chord you play the major of. For example, in the song "could i have this dance" by anne murray, near the end of the chorus it goes from D to Dm, and i'm not quite sure why that can work as well. I know music isn't set in stone, but i doubt the guitarist sat there cycling through chords seeing which one sounded the best, and i want to know why it works musically. Thanks to anyone who can help me =)
No - songs aren't 'supposed' to be limited to just 3 major chords. It's true that most songs in major keys contain 3 'naturally occuring' major chords (I IV & V). But other major chords are frequently found in songs as examples of:
1: Mode mixture - this means borrowing chords from the minor key. For example, chord VII (from the natural minor scale) is major. A song in C major might borrow this chord, which is Bb major.
2: Secondary dominants - (usually seen as 7th chords). These are chords that point to, and emphasise, another chord as a new tonic. It may just hint at it (called tonicisation) or it may force the song to change key (called modulation). For example D or D7 is used in the key of C to emphasise the chord G.
3: Chromatically altered chords (e.g., minor to major). These may cause a strong effect that requires resolution in the following chord or they might just be chords that don't have any harmonic function, but just sound good in a particular context. For example, the second chord of Dock of the bay in the key of G is B major instead of B minor. The out of key note in the B major chord makes the progression to the following C major chord all the more satisfactory.
Fretsource's reply covered the juiciest material but here's my 2 cents:
It seems like you are most familiar with the concept of major scale diatonic sequences [the I ii iii IV V vi vii0 thing]. That's a good starting point for learning how harmony works but it is faaaaaarrrrrrrrr from being the last word on the subject.
As you learn more songs you will tend to see similar techniques employed over and over. An example would be the use of a minor iv chord, or even a movement from the Major IV to the minor iv to the Major I. Happens all the time. Even Green Day knows that trick. So, figure out what the theoretical mechanism behind it is [in this case Mode Mixture] and put it into your bag of tricks. Then you'll understand it the next 50 times it happens.
Another example would be how classic rock bands like AC/DC play major chords based on the Pentatonic Minor Scale. That's the technique of taking the notes from, say, an E Pentatonic Minor scale [E G A B D] and making a chord progression from Major Chords based on those notes. Back in Black or T.N.T. are good examples.
If you start expanding your understanding of harmony now, in 5 years you'll be able to explain away many different non-diatonic chord progressions.
Oh yeah, and how about putting chords together just based on how they sound and saying forget the theory? Sometimes that can be a perfect change of pace. Music comes first, theory comes in latter to make sense of the mess.
Chicago Guitar, Bass, and Improvisation Teacher
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