Wordplay at work ~ Bertrand Russell

We have, in fact, two kinds of morality side by side: one which we preach but do not practice, and another which we practice but seldom preach.

I know that at one point I knew what this type of turn of phrase was called, but I’m afraid that I do not any longer. The closest that I can come up with is antithesis, though by definition it is close but does not quite fit.

Any clarification from anyone with a better memory than mine would be most appreciated.

EDIT: The structure is called a Chiasmus. Where a string is reversed and repeated, creating an AB:BA sort of structure. I wonder if that’s where the band name came from?
pyro