 Wiggins assumes that individuating a temporally enduring object involves being able to re-identify it at different times and under different descriptions. This assumption makes it possible to state substance individuation using the language of identity. Within the scope of this assumption, he makes two claims. The first is the sortal relativity of identity: that is, when any a and b are asserted to be the same thing, they must be the same something-or-other, and the something-or-other must be the kind of concept that answers ‘what is it?’ questions. In other words, there is no such a thing as ‘bare identity’—identity under no concept at all. Furthermore, the relevant concept must be an Aristotelian substance concept or sortal. More formally, this can be expressed as follows: