Finding the Key
Once you know all these structures you have a powerful tool to finding the
true key ( or keys ) of a piece of music and therefore which scale(s) to play
to improvise over the chords.
Songwriting and Composition
Some musicians use these structures without knowing them
at all — they just find that certain chords sound good together.
This is fine but if you consciously use the structures to write you may find
you can get ideas which you otherwise wouldn't have.
Remember that you can have
more than one structure in a song — indeed this is a good way to get "
light and shade " into a piece.
A commonly used rock device is to have a first section in a straight Major structure
then a second section using the Pentatonic Rock structure.
This can make the second section sound " heavier " than if you were
to launch into it straight away.
Another " light and shade " device is to have a Major section and
a Minor section in the same root key [ C major followed by C minor for example
]
Or you could have a minor section followed by a major section using the relative
major key
[ A minor followed by C major — ' Stairway to Heaven ' is an example of
this ]
A different example of this Minor to Major (and back again ) device can be found
in the Lou Reed track' Perfect Day ' — the verse of this song starts on
Bb minor then goes through a ' key changing style ' cycle of fifths sequence.
The chorus then comes in with a straight Bb Major key structure — this
gives a strong contrast in sound between the verse and chorus.
Memorizing Material
Once you start analyzing tunes with reference to the various
structures you may find that it's much easier to remember how the chord sequence
goes — so , for example , I can recall how to play ' Perfect Day ' by
simply remembering that it starts on Bbm — does the cycle of fifths routine
then changes to Bb Major for the chorus.
I don't necessarily have to memorize the whole chord sequence — just the
structure seems to be enough to bring the tune back even though I may not have
played it for a long time.
Working out your favourite Tunes
Many seemingly different songs actually use the same structural
devices — this can make working out chord sequences for yourself much
easier.
I can often predict what the next chords are going to be after hearing the first
few bars of a song that's completely new to me simply because the first few
chords fit into a known structure and so they are already , in a sense , familiar
to me.
Exercise
Analyze some of your favourite tunes with reference to the key structures.