FOM: SOL confusion

[Thomas Forster]

This post is admittedly partly the result of laziness on my part,
since i have not been following this thread in the detail it deserves.
Perhaps some kind person could summarise what it has uncovered. One
particular problem i have (and others have mentioned it too) is that
if there is nothing in SOL over and above ZFC then the reasons for it
cannot be straightforward: a complement of a property is a property
but ZFC has no axiom of complementation.  ZFC doesn't think that sets
are properties.   What philosophical reasons are there to suppose
that anything like this should be true?

       Thomas Forster