29.1Start with the problem created by the 3rd

Take G7:

G B D F

The note:

B

tells us very clearly:

G is a major-type dominant chord.

And B wants strongly to resolve:

B → C

So the 3rd carries a lot of functional information.

Now replace B with C:

G C D F

We get:

G7sus4

Suddenly the chord feels much less directional.