I am asked to show the following argument is valid:
I know you need to use the rules of inference like modus ponens/converse fallacy but I'm confused because it doesn't look like any of the forms I've learned about?
$$N\to B\lor S\\
S\to W\lor A \\
M\to N\land W \\
\text{therefore, }M\to B\lor A$$
I don't want to use the truth table because it will be real long. If someone can get me started i would really appreciate the help. thx
Best Answer
No valid argument can prove this. Suppose $M, N, S$ and $W$ are true, and $A$ and $B$ are false. Then the three premisses are all true, but the conclusion is false.