 More importantly, that there are no ad hoc sortals is essential to the significance of the formal proof that there is no such thing as relative identity. In logic and in the application of Leibniz’s Law, ‘a is F’ is normally equivalent to ‘a was, is or will be F’, otherwise the Law would not apply to such accidental properties as ‘is brown’. This is also the way phase sortals work: a human being is, was, or will be a baby. The argument against relative identity works by arguing that, if one allowed relative identity, a contradiction would follow, namely that one would get a situation in which a is G, a = b and b is not G. For this to be a contradiction, ‘is G’ must be univocal in both cases as either ‘—was, is or will be G’ or ‘—is at all times G’. For there is no inconsistency in a is, was, or will be G, a = b, and b is not at all times G. But if, whenever a contradiction is generated, one deems one of the sortals to be a phase sortal, and so to fall under the ‘is, was, or will be’ rubric, and the other to be the ultimate sortal which applies at all times, no contradiction will ever arise. All the cases of putative relative identity could be reconciled with Leibniz’s Law by deeming one of the sortals to be operating as a phase sortal in this instance.