Leibniz repeatedly daims to refute "Hobbes' doctrine of arbitrary truth". I argue against several recent expositors of Hobbes that Hobbes' view comes to nothing more scandalous than "nominalism" about kind terms. Although some have recognized that it is this thesis which Leibniz claims to refute, his argument has not been correctly understood. I maintain that the argument rests upon Leibniz' theory of signs and his account of concepts. In brief, Leibniz argues that concepts have structures which correspond to structures of (possible) things; thus, kinds are independent of language and truth is independent of arbitrary convention.