Reply #102: "The relationship between validity and truth depends upon one's definitions for each"

[SDuderstadt]

Wtf? We're talking about Logic, mhatrw. Your initial answer is made even more puzzling by your second sentence which, I suspect, you've cut and pasted from some Logic website and is essentially correct. Validity in Logic refers to structure and truthfulness is referred to as soundness. So, an argument, much as you describe, can be valid, in that it follows proper for, yet still not be sound (or true) because one or more of the premises are flawed. For example (and I am going to use a purposefully imflammatory example on purpose):

All "truthers" are stupid.
So-and-so is a "truther".
Therefore, So-and-so is stupid.

Valid, but not sound. Valid in that it follows the form:

All A is B
C is A
Therefore, C is B.

The argument is unsound (untrue) because the first premise is not true. All "truthers" are not stupid...it just seems that way.


Are far as your "question", it's because its antecedent is the negated consequent of its converse. Duh. I wouldn't waste a lot of time "testing" me on contraposition, mhatrw. I'm pretty sure I know far more about logic than you do, especially since I had to ask you my question numerous times over a long period of time before you could answer.