If/Then game #152

[AnnieM892]

Hi there, can someone please explain how to properly diagram this question/explain why it's diagrammed that way?

the question is as follows:

M will be picked unless N is picked.

it must be true that...
a) N --> -M (inncorrect)
b) -M --> N (correct)

[ohthatpatrick]

Sorry this slipped through the cracks.

The standard policy for "unless" is to treat it as "if not".

When we see, "M will be picked unless N is picked", we think
"If N is not picked, M will be picked"

~N --> M

When we write conditionals, we automatically write a contrapositive (if not the 2nd ingredient, then not the 1st ingredient).

So from
~N --> M
we would get
~M --> ~ (~N)


The "why" it's diagrammed that way is less important, to me, than is memorizing the automatic rule.

"Unless" is used to indicate a required or exceptional case.

REQUIREMENT:
You can't be President, unless you're at least 35 years old.

When we hear requirements, we can always truthfully say
"If you don't meet the requirement, you can't get/be the thing."

Thus, "If you're NOT at least 35 years old, you can't be President"

EXCEPTIONS:
The party will be great, unless it rains.

When we hear exceptions, we don't actually know what will be the case if the exception DOES happen, but we're sure about what will be the case if the exception DOESN'T happen.

Hence, "If it does NOT rain, then the party will be great".

Hope this helps.
which just means
~M --> N