In certaindiscourses, a know whether sentence is unacceptable when its answer iscommon knowledge as in (1). Similarly, an ever-free relative isunacceptable when the identity of its referent is known in some relevant way,as in (2).

(1) 

A: Don’tforget your umbrella. It’s going to rain today.

B: Yes, Iknow { #whether, that } it’s going to rain today. I heard the forecast.

(2)

A: Bill isbaking a pie.

B: Yes, and {#whatever, what } Bill is baking will be served for dessert.

A uniformanalysis is given for these observations that’s based on Heim’s (1991)principle of Maximize Presupposition, the idea that speakers have a preferenceto use the presuppositionally strongest usable utterance from a set of salientalternatives (i.e. to presupppose as much as possible).