only if, only when, only where

christine-2

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.

FixedDice

"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.

You do not know whether those sufficient and necessary conditions are the only conditions that are sufficient or necessary for the occurrence of the other. For all you know, there could be other conditions that come into play.

Suppose there is a rule in one of the states: "You can shoot another person with a gun only if that person is in possession of a gun." Per your logic, everyone who is subject to the rule would be able to shoot and kill people like gun dealers, police officers, and hunters who were trying to show their children the ropes. If you shoot any of those people and end up in the court for, say, voluntary manslaughter, the judge may not be very impressed with that particular interpretation. Chances are there are other conditions that allow one to resort to that rule -- like seeing someone else break into his or her place of residence with a gun in his or her hand(s), for example.

If all else fails, I would say this is one of those things you just have to accept and move on. You know, kind of like "one plus one is two."