 The term ‘criterion of identity’ is ambiguous. In an epistemological sense, a criterion of identity is a way of telling whether an identity statement is true, or a way of recognizing whether an individual A is identical with an individual B. However, the notion of a criterion of identity also has a metaphysical interpretation, according to which it is a set of (non-trivial) necessary and sufficient conditions for the truth of an identity statement. Although a criterion of identity in the second (metaphysical) sense might supply us with a criterion of identity in the first (epistemological) sense, it seems that something could be a criterion of identity in the second sense even if it is unsuited to play the role of a criterion of identity in the first sense.