LSAT Logic Games | Conditional Logic | Only if, Unless

6 Comments

1. If “if and only if” signals a biconditional statement, doesn’t that mean it actually is true both ways (positive, converse, inverse, and contrapositive?)

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2. I still don't understand chow can " R is ranked 5th only if E is ranked first." Produce the same diagram as "Only if E is first can R be 5th."

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3. To be honest, for the "Unless" part, what I usually do is just automatically cancel out "not" and read it as is. And if there was no "not", then I would add one. That's a formula I essentially use. I also appreciate that you said "unless" introduces a necessary condition. I feel like that was super helpful!

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4. In short, "Only if" is a straight arrow —->.
   Unless is: "If Not" and goes on the left. Crystal clear 🙂

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5. I’m so confused with the “only if” example. “Rakesh is ranked fifth, only if Eustace is ranked first.” So to me that means the same thing as saying……If Eustace is ranked first, then we know Rakesh is ranked fifth. Why is that not so??
   How are “if” and “only if” different? I get the umbrella and US president example. What doesn’t make sense is the diagram on this example. If I read that rule, I would diagram it – if E1—->(then) R5.
   In the video while you diagram you actually say, “If Rakesh is 5th then Eustice is 1st.” That seems like the opposite of the rule.

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6. This is really insightful….so that means this link uses unless incorrectly?

   In this https://youtu.be/lRpdvYbZLTg and also https://youtu.be/CV68q9rPBTI?

   Also it would be great if you could let me know why interpreting ‘if B then not A’ from ‘A unless B’ is not logically correct as it sounds valid

   For example ‘I will go to school unless it rains’ doesn’t it imply that the exception of me going to school is when it rains I.e if it rains then I will not go to school

   This is pretty confusing…I would appreciate it if you could help

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