"If, but only if:" same as "if, and only if"?

jstrummer1977

"If, but only if:" same as "if, and only if"?
« on: February 04, 2005, 11:32:42 AM »
Is "If, but only if" the same thing as "If, and only if"?

This comes from the last game of the Dec. 2004 LSAT:

"Nation X exports soybeans if, but only if, Nation Y does also."

At first I thought it would be X<-->Y. Then I thought the "but" instead of "and" makes it Y-->X. But if that's the case, then there's no answer for question 20.

Just trying to firm up my thinking b/f February. If anyone else can confirm/deny, that would be great.

Thanks.

cascagrossa

• 2424
Re: "If, but only if:" same as "if, and only if"?
« Reply #1 on: February 04, 2005, 11:36:06 AM »
either way will give you 100% right on that game(i did it only as "only if"), but in logic they mean the same thing and are both biconditionals.

A.J

Re: "If, but only if:" same as "if, and only if"?
« Reply #2 on: February 04, 2005, 11:36:27 AM »
Yes its the same.

Think about it this way: A will exist but only if B exists.

So for any B there must be a corresponding A, and if there is an A it must have a companion B.

Another tricky wording of the same thing that I saw come up in a LR question is "A is any B".  That says the same thing.

amarain

• 4007
Re: "If, but only if:" same as "if, and only if"?
« Reply #3 on: February 04, 2005, 11:39:43 AM »
Yes its the same.

Think about it this way: A will exist but only if B exists.

So for any B there must be a corresponding A, and if there is an A it must have a companion B.

Another tricky wording of the same thing that I saw come up in a LR question is "A is any B".  That says the same thing.

This is what I don't understand. A will exist but only if B exists. But why can't B exist without A?

A.J

Re: "If, but only if:" same as "if, and only if"?
« Reply #4 on: February 04, 2005, 11:41:09 AM »
Sorry, I left an "if" out.

I should have said A will exist IF B exists, but only if B exists.