Tuesday, January 30, 2007

What Is a Valid Argument?

As part of the basic concept series, Janet Stemwedel explains arguments [Basic concepts: arguments]. For example, she says,
Here's an example of a valid argument:
1. Britney Spears is from Mars. (premise)
2. Martians have astounding vocal range and are great dancers. (premise)
3. Hence, Britney Spears has astounding vocal range and is a great dancer. (conclusion)
Are you convinced that this is a valid argument?


  1. Clearly she is drawing a distinction between a "valid argument" and a "true argument." Yes, the conditional is valid. IF BS were from Mars AND Martians had singing and dancing skills, then the conclusion would follow.

  2. She explains it in her post--it's valid argument, but it's not a sound argument.

  3. This is a common reaction to the distinction between a sound and a valid argument. Validity just means that the logical structure is correct - if the premises are true, the conclusion must be true. Of course, if the premises are absurd, then the argument is not sound (although it might still be true).

    Formal logic and critical thinking force us to understand the logical relations between statements used in arguments. They do not give us a magical way to find truth. You need to start with some measure of truth first, before an argument will give you any.

  4. The distinction is important. I struggle constantly with trying to explain to students the difference between logically valid arguments and rational (sound) arguments.

    There were lots of valid arguments for invading Iraq, for example. They were valid but stupid.

    Janet did us a favor by posting a clear explanation. I hope people pay attention.

  5. Sadly it's all too easy to construct a valid argument for most any position on nearly any issue. Rush Limbaugh, for example, does it all the time -- so do Holocaust deniers. The often tragically hard part of putting an argument together is that bit about soundness.