A class is a generalized set invented to get around Russell's antinomy while retaining the arbitrary criteria for membership which leads to
difficulty for sets. The members of classes are sets,
but it is possible to have the class of "all sets which are not members
of themselves" without producing a paradox (since
is a proper
class (and not a set), it is not a candidate for membership
in ).
of "all sets which are not members
of themselves" without producing a paradox (since
is a proper
class (and not a set), it is not a candidate for membership
in 
).
