Abstract

It is common to argue that something x is distinct from something y by pointing out that x and y do not share all their essential properties. I show that arguments of this type are unsound. This unsoundness is rooted in the fact that sentences of the form ‘x is essentially F’ are ambiguous. Under one reading, the sentence says of x that it has a property of a unique and special kind. Interpreted in that way, the sentence is false, for there are no such properties. Under another reading, the sentence says of x that it has a property and adds that this property is essential to x. Interpreted in that way, the sentence may be true but it does not allow to reach the desired conclusion that x is distinct from y. Thus, if someone argues that x is distinct from y by pointing out that x and y differ in essential properties, they face the following dilemma: either one of the argument’s premises implies the existence of the special property and it is false, or none of the premises implies the existence of the special property and the argument is invalid.