relative identity

The view advocated by the 20th-century English philosopher Peter Geach according to which the identity statement ‘ a = b ’ needs interpreting as ‘ a is the same F as b ’ where F is a kind-term or sortal . The clearest motivation for this view would be if different choices of sortal produce different identity statements with different truth-values. Thus if a denotes a statue at an early time, and b a statue at a later time, it may be that a is the same mass of clay as b, but not the same statue. However, it may also be that the choice of sortal is prejudged in the meaning of the names a and b, in which case no such discrepancy can arise, although sortals are still playing an important role in evaluating identity statements.