Published in Philosophical Quarterly 56 (2006), 39–54.
Abstract: The article is an investigation of a certain form of argument that refers to Leibniz’s Law as its inference ticket (where Leibniz’s Law is understood as the thesis that if x=y, then all properties of x are properties of y, and vice versa). Arguments of this form are often used to establish certain categorial distinctions, e.g. a distinction between kinds and properties, or a distinction between processes and events. But it is shown that and why there can be deficient arguments of this form. It is then argued that the interesting philosophical cases of this argument form are unconvincing since they cannot be seen as clear cases of the unproblematic variety of this argument form.