 The puzzles about identity outlined in §2 (and there are many others, as well as many variants of these) put considerable pressure on the standard account. A theory of identity that allows for instances of RI is an attractive alternative (see below §4). But there is a certain kind of example of RI, frequently discussed in the literature, that has given relative identity something of a bad name. The passenger/person example is a case in point. The noun ‘passenger’ is derived from the corresponding relational expression ‘passenger in (on) …’. A passenger is someone who is a passenger in some vehicle (on some flight, etc.). Similarly, a father is man who fathers someone or who is the father of someone. This way of defining a kind of things from a relation between things is perfectly legitimate and altogether open-ended. Given any relation \(R\), we can define ‘an R’ to apply to anything \(x\) that stands in \(R\) to something \(y\). For example, we can define a ‘schmapple’ to be an apple in a barrel. All this is fine. But we can’t infer from such a definition that the same apple might be two different schmapples. From the fact that someone is the father of two different children, we don’t judge that he is two different fathers. The fact that airlines choose to count passengers as they do, rather than track persons, is their business, not logic’s.