1. ## question about validating an argument

I am trying to detrmine whether this argument is valid or not:

p → q
∼p
———
∴∼q

I did not see this as modus ponens or modus tollens.

But I described it as:

p: I walk my dog
q: he is happy

p → q: if I walk my dog he is happy
~p: I did not walk my dog

therefore

~q: he is not happy

This is not valid according to the table there could be two different outcomes.

is this correct?

p|q|p → q| ~p|~q

T|T|T |F |F
T|F|F |F |T
F|T|T |T |F
F|F|T |T |T

Is this correct?

If now please explian how to prove (valid) or (invalid)?

2. Let $\displaystyle P:x>3$ and $\displaystyle Q:x-1>0$.
If $\displaystyle x=2$ you have $\displaystyle \neg P$ do you have $\displaystyle \neg Q?$

3. yes

4. Originally Posted by robasc
yes
Yes what?

You have $\displaystyle \neg(2-1>0)?$

5. yes it is false

6. Well then the argument is not valid.

7. this is known as a fallacy, denying the antecedent correct?

8. Yes. What is the point of all this?

9. I am double checking myself to make sure I am understanding the material correctly?