Thread: A rules of inference question

This might be easy for some, but I seem to be having a bit of trouble grasping the concepts behind rules of inference.

Given the premises “if it doesn’t snow or if the roads are clear, then I will drive to Montreal and visit my sister,” “if I drive to Montreal, I can visit a museum,” and “I do not visit a museum,” use the rules of inference to determine whether or not “It snowed” is a valid conclusion.

Originally Posted by Runty

Given the premises “if it doesn’t snow or if the roads are clear, then I will drive to Montreal and visit my sister,” “if I drive to Montreal, I can visit a museum,” and “I do not visit a museum,” use the rules of inference to determine whether or not “It snowed” is a valid conclusion.

Forget the sister bit. It has nothing to do with question.


Now you supply reasons.

Originally Posted by Plato

Forget the sister bit. It has nothing to do with question.


Now you supply reasons.

That does help a bit, but I could use a bit more detail (these rules are a bit difficult to wrap my head around). Does your answer show that the conclusion is valid or invalid?

It snowed is valid.
We use modus tollens twice.
Then simplification.