I am beginning to appreciate more the comments provided by Anthony (if only he would think before commenting, and not endlessly comment and delete - bear in mind that any comment whether deleted or not comes through my email box).
I suggested earlier that some things used to exist, but no longer exist. Given my acceptance of Brentano's equivalence - that "some A is B" is equivalent to "Some A that is B exists", Anthony has spotted that this entails that some things are no longer things, and are thus not things (although, to be sure, they were things). And indeed some men (e.g. Caesar) who were a man, are no longer a man. Ergo, some men are not men.
This has the distinct whiff of paradox, which I will investigate later.