GUEST is right about the matter of irrelevance. If one knows the biases of the person making the assertion, one has good reason to question the truth of the assertion.

If I hear it on Fox News or from Rush Limbaugh or Ann Coulter, I would check the truth of their statements on independent sources.

PERHAPS what they're saying is true. But WHO THEY ARE and having knowledge of their biases and prejudices is reason enough to doubt the veracity of their statements, and calls for independent checking.

The principle of argumentum ad hominem is, of course, valid. But demanding evidence and verification because you have found the person making the assertion to be chronically untrustworthy is ALSO valid.

Philosophy 115--Logic.

Don Firth