The set of unhappy families would, I suppose, be an example of what Wittgenstein calls a family, since each unhappy family is unhappy in its own way, this not evidently preventing them from each being called an unhappy family. And happy families, being all alike, perhaps compose a class that is closed under
necessary and sufficient conditions.
A similar, (…) argument against definition is the inductive argument. (…) [it] claims that this attempt to define art has failed, that attempt has failed, . . . , so the next attempt will probably fail.