 Other researchers have argued that autonoesis is a contingent feature even of episodic memory. This would undermine its status as a criterion of episodicity, but, regardless of whether autonoesis is taken to be a necessary or only a contingent feature of episodic memory, it is not immediately obvious why we should be capable of autonoetic episodic memory—as opposed to mere what-where-when memory—at all. Indeed, accounting for any form of episodic memory in functional terms has proven to be a difficult challenge, and researchers have proposed a range of past-oriented, future-oriented or counterfactual, and metacognitive accounts.