Hey Janet,
I know how it feels getting "stuck in a rut". Try this...
Basic chord substitutions - for simplicity's sake I'll give examples in C.
There's a simple formula which goes like this:
1, 3, 6
2, 4
5, 7
Those are scale degrees. So if you have a C major chord, you can substitute it with an Em or Am and vice-versa. In essence, C, Em and Am are interchangeable. This depends on your melody of course and you would need to play it by ear, as it were.
Same for 2, 4 - Dm and F; and 5, 7 - G and Bdim (or half-diminished).
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****ing things up... EDIT - that's interesting, after I posted, this word got censored. It was only the word "S-p-icing" :)
Precede your chords with their Dominant 7ths.
The full formula is: 4, 7, 3, 6, 2, 5, 1. It's a sort of Cycle of Fifths. Here's how it works.
For starters these are not scale degrees based on the Home key (C) but based on the chord you want to go to. That chord becomes the '1'.
The simplest example would be if from C you want to move to F. So you play, C to C7 and then go to F. (C is dominant of F = 5, 1)
Or from C to E - you would play C, Bdim and then E (think Yesterday, Beatles). (B is dom to E = 5, 1)
C to Am - C, E7 then Am. (E is dom to A = 5, 1)
To go further (backward in the formula) then you could play:
Keeping same eg of C to F: -
Gm, C7, F = G is 2nd degree of F, C is 5th, F is 1 = 2, 5, 1.
Even further back i.e. 6, 2, 5, 1 (same eg)
Dm, Gm, C7, F = D is 6th degree, G is 2nd, C is 5th, F is 1 = 6, 2, 5, 1.
Get the idea? :)
There there are the infamous Tritone substitutions - the jazzy stuff.
If you want to go from C to F you play: -
C, F#7 (or F#13th if you want to be more colorful) and then F.
This works best with what are called Functioning Dominants.
Func Dom are 5-1s as explained above. I.e. C7 to F or E7 to A, or Ab7 to Db, etc...
Non-Functioning Dom. are all those dominant 7th chords that DO NOT resolve to their 1. For e.g. E7 to F (like the chorus in Imagine). Or B7 to G... etc... So Non Func Dom are those "5s" that do not go to 1.
So back to Tritone Subs...
They are called Tritone because they are 3 whole-steps away. So Tritone (TT) of C would be F# because:
C, D, E, F# - there is a whole step in between each note.
Also notice that you only need to memorise 6 TTs because if C is TT to F#, then F# is TT to C.
So another example if you're playing in C:
You're on the G chord and about to go to the home key (C) - so from G, you go to Db7 and then C.
G is TT to Db - G, A, B, Db.
An easy way to remember TT is to think of them as #4 or b5:
TT of C = 4th of C which is F + 1 (#4) = F#.
or
TT of C = 5th of C which is G - 1 (b5) = Gb or F# (same thing)
TT of G = 4th of G which C + 1 (#4) = C# (Db)
or
TT of G = 5th of G which is D - 1 (b5) = Db (C#)
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I know this might be a lot to digest but I can assure you it will open a new world of possibilities for you :)
If you need any clarifications just ask. I'd be happy to help :)
Sam