Writing -- identity conditions for languages

So -- my Epistemology & Metaphysics paper is turning out to be about the identity conditions for a language....

Anybody have a suggestion about good lit on it? I have some stuff and what could be a really good article from the 70s coming in ILL.... this isn't exactly a hot topic -- but I think it is interesting enough to get me past my requirement :).

The question is kind of like this: When do differences in a natural language become evidence of a distinct language and not a dialect?

The intuitions go like this...

a) hubby and I speak the same language and the same dialect within the language --- we share vocabulary, pronunciation, grammar etc... (even the MN grammar of "I'm going to the store, do you want to come with " being correct and the vocabulary of using "pop" to designate carbonated beverages".)

b) We can easily communicate with English speaking Canadians, even though their dialect is different. They may pronounce things differently, use "eh" when we can't get the hang of when to say it etc... but, generally myself, hubby and the Canadian all speak the same language.

c) Hubby and I don't speak the same language as French Canadians (although, there is a great camping story from a few years ago in which hubby, via a red-neck from Manitoba, helped a French-only speaker get his camper out of a tight spot..) -- clearly, he needed an interpreter.

Each of these instances (A-C) are pretty clear -- A and B are instances of same language, C is an instance of a different language... but, what makes it different.... we need a hard case.

The hard case can be American Sign Language (ASL)-- I took an ASL class a few years ago, it was very difficult and very fascinating... I'll talk about it later...

so the intuition on ASL is a bit more complicated... the options are:

d 1) ASL is like braile, another way to communicate English. Instead of speaking, ASL users use their hands. Instead of hearing, ASL users use visual clues. In formal communication, the deaf community uses standard English. Their speech performance is more like a dialect than anything else.

d 2) ASL is a distinct language from English. It has a distinct set of terms and phrases, some of which are not translatable into English. It also uses grammar more closely associated with French than English. Finger-spelling is the only way in which it is signifcantly different than English, and that is a small part of ASL.

What I'm looking for (or, need to invent... hmmm) is a theory that will put A and B on one side, C on the other and make a decision about ASL.... my own intuition says that d 2 is correct, ASL is a separate language.

The thing is that it isn't enough to say that distinct vocabularies and/or different grammars are enough to make that distinction between languages because dialects differe in vocab and grammar and distinct languages can share big parts of vocabularies and by grammatically similar to one another. Further, within the same language two or more distinct grammars could be functioning...

The Political Philosopher in me likes the real answer I'm probably going to end up with -- namely that the differences are really cultural....

Thoughts?? It is going to be a looooong day....