 On this picture, knowledge involves discrimination: in order to know that an object o is F, one must be able to discriminate o from things that are not F. Knowledge gives the agent this ability insofar as it involves an awareness-episode that puts the agent in touch with a genuine feature of the object o in virtue of which she can distinguish o from non-Fs. We can see how this definition rules out cases like Shells, Mist, and Horns. In Shells, since the agent’s awareness-episode arises from a blind guess, he or she isn’t aware of any distinctive mark X in virtue of which she could tell whether the number of shells in the gambler’s hand is five rather than, say, three or four. Similarly, in Mist, the agent mistakes mist for smoke. Even though smoke is a distinctive mark of fire, the smoke that she ascribes to the mountain isn’t a property that the mountain actually has. Finally, in Horns, the agent infers that the animal before her is a cow on the basis of the fact that it has horns. But horns aren’t a distinctive mark of cows.