13.28Tensions versus extensions

Jazz theory often calls 9, 11, and 13 tensions.

That doesn't mean they necessarily sound unpleasant.

It means they extend the basic chord beyond 1-3-5-7.

Some are highly consonant.

Others create stronger color.

For example:

D over Cmaj7 = 9

usually gentle.

F over Cmaj7 = 11

more problematic because of E-F.

F♯ over Cmaj7 = ♯11

a distinctive luminous sound.