Both arguments are based on the breakdown of normal criteria of identity in certain science-fictional circumstances. In one case, normal criteria would support the identity of person A with each of two other persons, B and C; and it is argued that, in the imagined circumstances, ‘A=B’ and ‘A=C’ have no truth value. In the other, a series or ‘spectrum’ of cases is tailored to a sorites argument. At one end of the spectrum, persons A and B are such that ‘A=B’ is clearly true; at the other end, A and B are such that the identity is clearly false. In between, normal criteria of identity leave the truth or falsehood of ‘A=B’ undecided, and it is argued that in these circumstances ‘A=B’ has no truth value.