case in point
In point. Not and point. There aren’t two things.
-
Wrong: Case and point: last quarter.
Right: Case in point: last quarter.
One thing—a case that’s in point, meaning pertinent. And implies two.
The phrase
In point is an older English construction meaning “relevant” or “to the purpose”—it survives in case in point and in the legal phrase in point of fact.
So a case in point is a relevant example. Case and point would be two separate things, which is not what anyone means and not a phrase.
Spoken quickly, in and and are almost indistinguishable, which is how this one spreads.
Now go make a relevant one.