 We noted above that most if not all accounts of acting for a motivating reason require as a condition that the agent be in some kind of epistemic relation to the reason that motivates her. And we saw also that a widespread view is that this epistemic relation is one of belief: for an agent to act for the reason that p, the agent must believe that p. It is this thought that led many to endorse the view that reasons are mental states (often as part of the “desire-belief” conception of reasons for action described above). But the view that mere belief is not sufficient to act for a reason has gained popularity in recent years. And many have argued that, in order to act in light of a fact that is a reason, an agent needs to  know the relevant fact. The view is explicitly defended by Unger (1975), Hyman (1999, 2011 and 2015), Williamson (2000 and forthcoming), Hornsby (2007 and 2008 (as part of her disjunctive conception mentioned above)), and McDowell (2013)—but many others also endorse it. The basic idea behind this position is that an agent may act on the basis of a belief merely by treating that belief (i.e., what she believes) as a reason for acting. However, if there is a fact in virtue of which her belief is true, then she acts in light of that fact, or is guided by that fact, only if she knows that fact. If the agent does not know the fact, we cannot say that she was guided by it (Hyman), or that she was responding rationally to it (McDowell). If the agent does not know the fact, the argument goes, the relationship between the agent’s acting as she did and the fact is fortuitous, a matter of luck or coincidence, and hence not sufficient for the fact to be her reason for acting. And this, they argue, is so even in cases where an agent acts motivated by a belief that is both true and justified. For just as Gettier (1963) showed that having a justified true belief is not sufficient for having knowledge of the corresponding fact, so, these authors argue, acting on a justified true belief is not enough for acting in light of the corresponding fact: the connection between the fact and the action is fortuitous. (See entries on  the analysis of knowledge  and  epistemology  for discussions of Gettier’s arguments).