Epistemic impossibility states that when a person makes a statement, that statement is epistemically impossible if it cannot be true, given what we know. All of this is based on the knowledge available to us. This states that the statement cannot be true according to our current knowledge. A statement is said to be epistemically possible if it could be true according to the knowledge we currently have.
Also, a statement can be epistemically necessary if it is certain or it must be in the given situation according to the current knowledge available to us. Epistemic impossibility is when a statement simply cannot be true given the base of knowledge we currently have available to us at the present time.