Morris Weitz and Definitions

Can Morris Weitz’s idea about defining art truly be applied to music, literature, and other popular art-related domains? Does this make for a sufficient definition? For anyone who doesn't know, Weitz came up with the idea of having a kind of umbrella term for "art", making the actual definition of "art" impossible, but being able to define the sub-categories of "art" which all bear a kind of "family resemblance" to each other. I personally liked this idea in terms of art, but I was wondering how many other things this kind of concept could be applied to. I think it would be very helpful in relation to trying to find a good definition for "fiction". It would be much easier to define fiction in the specific, Sci-Fi movies for example, rather than in the general. After we identified and defined the various sub-categories for "fiction", we could then go on to determine whether or not "fiction" itself is definable. If it is, it can be defined in relation to the sub-categories. And, if it is not definable, at least we can define specific types of fictional works.