I think "A if, but only, if B" says something different from "A if and only if B." All "if and only if" statements can be parsed into a conjunction of two stipulations: (keeping your variables) A if B
and A only if B (i.e., A as necessary and sufficient conditions, respectively).
It is true that in most semantic contexts, "but" serves to emphasize an otherwise uninteresting conjunction (I studied little and I passed vs. I studied little *but* I passed); in this case, however, the "but," set off in a restrictive relative clause, constrains the meaning. I think in effect, the "but only if" part of the statement "swallows" up and replaces the "if" part of the statement. It is as if the speaker corrected himself mid-sentence.
For instance, if your annoying cousin nagged you about taking him to swim, you might say "okay, if you finish your homework." If you said that, you would be promising to take him to swim once he finished his homework. But you could be sneaky and say "Only if you finish your homework," in which case no promise would have been uttered. I think "A if, but only, if B" approximates this sense more than the former (just repeat the following statements--they do sound like they mean different things:
okay, if you finish your homework VS.
okay, if, BUT only if, you finish your homework. Otherwise, it's just redundant (why would you say, in normal linguistic contexts, that something is both a necessary and sufficient condition if it is going to be sufficient either way?--it serves only to confuse your poor cousin!).
Having said this, I am not certain, however, if I am right (or if there is a right answer). A if, but only, if B, is not a conventional usage. It's ambiguous, because I have a feeling (going by previous posts) that our intuitions do diverge here. It shouldn't be on the LSAT, IMO. They should stick with the traditional IFF (if and only if) construction. I think we will just have to accept whatever opinion LSAC has about this.
So does anyone who recently took the test know which side they're on?
