P: If you climb mountains, you will not live to a ripe old age.P: But you will be bored unless you climb mountains.C: ?

Moreira-Tetauira July 26, 2019

Necessary condition rule

I found B>not CM for the second premise. Why was it wrong? I thought that unless just introduces a necessary condition. Thank you

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Irina July 26, 2019

@Moreira,

X unless Y is properly diagrammed as:

~Y >X

If NOT Y, THEN X

or

~X > Y

IF NOT X THEN Y

These are logically equivalent statements.

If you climb mountains, you will not live to a ripe old age

CM > ~L

But you will be bored unless you climb mountains.

~CM > B or
~B > CM

It is true that "unless" introduces the necessary condition, but the other part of the conditional statement must be negated to become sufficient condition.

Does this make sense?

Let me know if you have any other questions.