How can you tell if an argument is valid?

Question

maryvite · Answer

Valid arguments are always sound.
The premises lead logically to the conclusion.
Valid arguments are never sound.
There are two premises and a conclusion.

Eiwoh2 · Answer

Usually if that argument is accompanied by credible sources, and is well developed. But i would say with teh answer choices, valid arguments are always sound.

maryvite · Answer

How do you know which counterargument to address?

I choose the weakest counterargument to make my argument look better.
I select the strongest or the most popular counterargument.  
Actually, it is best never to mention counterarguments because they are a distraction. 
I use the first one that comes to mind.