If an object fell under more than one ultimate sortal, there could be a time at which the object satisfied the criteria for one sortal and not for the other

The conclusion is striking because it is a denial that a and b might be identical under one form of identification, but not under another. In fact it implies that every individuable object falls under just one ultimate sortal. (Wiggins admits this in 2001: 67 n.7. What is meant by ultimate sortal will emerge below.) For every ultimate sortal has its own principle of individuation, and if an object fell under more than one, there could be a time at which it satisfied the criteria for one and not