 Ordinary challenges to judgments or claims, including claims to know, are sometimes invitations to detail our credentials—our possession of appropriate acumen in making judgments of the type in question. Sometimes, however, they are invitations to detail our facts—the features of the circumstance that figure in our judging in the way that we do. For example, we might claim to know that that presented thing is a goldfinch “by the shape of its head”. If we were to detail our facts in that sort of way, then we might be open to further challenge: someone might claim that that’s not enough of a basis on which to judge that the presented thing is a goldfinch. In addition to emphasizing the role of special acumen in this type of case—not just anyone can tell a goldfinch by the shape of its head—Austin makes two important claims about such potential challenges to our facts. First, Austin claims that, in order for such a challenge to be appropriate, the challenger must have in mind some more or less definite lack, for example by pointing out that birds other than goldfinches have heads of that shape. Second, Austin writes: