Say you have premise that doesn't specifically identify whether members are in or out, but is a bi-conditional like:

"Wharton serves on a different committee than the one Zhu serves on"

How do you decide which side to negate? It ends up having consequences when you chain up and try to find "or" and "not both" inferences with other members. I'm so confused.

I am not understanding the key concept of "only if/only when/only where" and how they are not biconditionals. Can someone help?

take this sentence:

"Lagitha performs fifth only if Norton performs third."

from the rules, I understand the translation to be:

L=5--------->N=3

BUT i don't understand for the life of me why. They seem to be biconditional.

As in: "Lagitha can perform anytime she wants unless norton is third, and in that case, she must be 5th." Confirming the necessary in this case, actually confirms the sufficient.

It seems to me that the english sentence

"If Lagitha performs 5, norton performs 3" has an entirely different meaning.

I thought i could just muddle through not understanding this, but now "only if" comes up all over logic games. I have tried just memorizing the rule, but it would be so much better to actually understand it. I have gone over all the lessons from this group, and I still don't get it. I'd really appreciate any advice.