Can somebody explain chord changes?

[Keyzislife]

I would like to know what exactly are chord changes, what are their purpose?

[berbie]

You asked a very general question, keyz.  Chords changes lead to progressions simply put.  Or did you mean chord substitutions?  Or do you mean, "Which chords are in a progression and why"?

[Keyzislife]

I'm talking about chord subsututions

[berbie]

One type of substitution is the tri-tone substitution.  A tritone is two notes which are three full steps apart.  Example,  F-B.  Two dominant seventh chords will substitute for one another if the root notes are a tri-tone apart.  F7 substitutes for B7 and vice versa.  G7 substitutes for Db7, and so on.  There are 6 tri-tone substitutions.  A person could memorize them, but remembering the formula is probably sufficient.  Or even better, I will post them.

F7-B7-F7

E7-Bb7-E7

Eb7-A7-Eb7

D7-Ab7-D7

Db7-G7-Db7

C7-Gb7-C7

[T-Block]

Chord changes are pretty much that, the order that you play the chords in. Each movement from chord to chord is a change, hence the term "chord change".

[berbie]

To use a tri-tone sub in a 2-5-1 you simply play a seventh chord 1/2 step above the one. You play the two minor, then the sharp one seventh chord and then the one.  Example:  Key of C.  D minor, Db7, C.  The Db7 would be the tri-tone sub for the G7. Try it and see how it sounds to you.  Of course, there are other uses.