We call hard information, information that is veridical, fully introspective and not revisable. This notion is intended to capture what the agents are fully and correctly certain of in a given interactive situation. At the ex interim stage, for instance, the players have hard information about their own choice. They “know” which strategy they have chosen, they know that they know this, and no new incoming information could make them change their opinion on this. As this phrasing suggests, the term knowledge is often used, in absence of better terminology, to describe this very strong type of informational attitude. Epistemic logicians and game theorist are well aware of the possible discrepancies between such hard “knowledge” and our intuitive or even philosophical understanding of this notion. In the present context is it sufficient to observe that hard information shares some of the characteristics that have been attributed to knowledge in the epistemological literature, for instance truthfulness. Furthermore, hard information might come closer to what has been called “implicit knowledge” (see Section 5.3 below). In any case, it seems philosophically more constructive to keep an eye on where the purported counter-intuitive properties of hard information come into play in epistemic game theory, rather than reject this notion as wrong or flawed at the upshot.