 Some philosophers reject the Gettier problem altogether: they reject the aspiration to understand knowledge by trying to add to JTB. Some such philosophers try to explain knowledge in terms of virtues: they say that to know a fact is for the truth of one’s belief to manifest epistemic virtue (see Zagzebski 1996 and Sosa 1997). Other such philosophers try to explain knowledge by identifying it as a genus of many familiar species: they say that knowledge is the most general factive mental state operator (see Williamson 2002). And still other such philosophers try to explain knowledge by explaining its distinctive role in some other activity. According to some, to know a fact is for that fact to be a reason for which one can do or think  something.[19]  According to others, to know a fact is to be entitled to assert that fact (see Unger 1975, Williamson 2002, DeRose 2002 for defenses of this view; see Brown 2008b and 2010 for dissent). According to still others, to know a fact is to be entitled to use it as a premise in reasoning (see Hawthorne &amp; Stanley 2008 for defense of this view; see Neta 2009 and Brown 2008a for dissent). And according to still others, to know a fact is to be a trustworthy informant concerning whether that fact obtains. Finally, there are those who think that the question “what is it to know a fact?” is misconceived: the verb “to know” does not do the work of denoting anything, but does a different kind of work altogether, for instance, the work of assuring one’s listeners concerning some fact or other, or the work of indicating to one’s audience that a particular person is a trustworthy informant concerning some matter (see Lawlor 2013 for an articulation of the assurance view, and Craig 1990 for an articulation of the trustworthy informant view).