Philosophy, Logic question please

Question

1 All dogs are Marsupials.

Lassie is not a marsupial.

Therefore, Lassie is not a dog.

2 Either you love the President, or else you are a terrorist.

James doesn’t love the President.

Therefore, James is a terrorist!

For number one does it fall under modus tollens or pones?

Answer 1

Modus ponens arguments have the following structure:

If A then B

A

Therefore, B

Modus tollens arguments have the following structure:

If A then B

Not B

Therefore, not A

We can check if your arguments are either of these forms by replacing the content of the argument with letters like 'A' and 'B'.

Let A = something is a dog, let B = something is a marsupial

All dogs are marsupials = If A then B

Lassie is not a marsupial = ~B

Therefore, Lassie is not a dog = ~A

So, the structure of the first argument is:

If A then B

~B

Therefore, ~A

So it is modus tollens.

Answer 2

1. Proof by contradiction. Assume Lassie is a dog. Then Lassie must be a marsupial by first sentence. But we know Lassie isn't, therefore our first assumption must be wrong (that she is a dog). So Lassie isn't a dog.

Modus ponens : P implies Q, Q is true, so Q is true

Modus tollens : If P then Q. Not Q, so not P.

So (1) is modus tollens. P = dog, Q = marsupial