My goal here is to assess whether Wittgenstein’s metaphilosophical conception of a descriptive philosophy is in accordance with his philosophical practice. I argue that Wittgenstein doesn’t really limit himself to description when he criticizes Moore’s use of the verb “to know”. In On Certainty, Wittgenstein argues that Moore’s claims of knowledge (such as “I know I have two hands”) are at odds with the everyday use of the verb “to know”, because, among other things, they don’t allow the possibility of justification. That is, Wittgenstein considers that proper, everyday claims of knowledge require the possibility of justification. What I try to show is that this idea cannot be derived from the mere observation and description of knowledge claims in ordinary language. I conclude that Wittgenstein’s treatment of the verb “to know” constitutes an inconsistency between his metaphilosophical posture and his philosophical practice.