Valid vs. Sound Arguments

[Math Is Hard]

I need a little clarification on some terminology being used in my crit. reasoning class: valid and sound.
Is a valid argument the same thing as a sound argument?
Or can you have a valid argument that is actually unsound?

Thanks!

[Tom Mattson]

Is a valid argument the same thing as a sound argument?


No, an argument is valid if it is deductively valid. That is, if the premises necessarily imply the conclusion. But a valid argument need not have true premises. An argument is sound if it is valid, noncircular, and contains only true premises. In that case, the conclusion is not only necessarily implied by the premises, it is also necessarily true.

You may find these threads helpful:

Logic (http://www.physicsforums.com/showthread.php?t=33&page=1&pp=20)
Logic Notes (http://www.physicsforums.com/showthread.php?t=111)

In posts 4, 5, and 6 of Logic Notes, I go into detail about validity and soundness.


Or can you have a valid argument that is actually unsound?


Yes, here's an example:

If 2+2=4, then Greg Bernhardt wears miniskirts.
2+2=4.
Therefore, Greg Bernhardt wears miniskirts.


It's perfectly valid, because the schema is valid:

p-->q.
q.
Therefore, q.

But are the premises true? I don't want to find out. :rofl:

[Math Is Hard]

Thanks for the help, Tom. The only problem now is going to be controlling the giggling during the exam when I start thinking back to your example! :rofl: