"Poisoning the Wells" as logical fallacy?

[Speaker for the Dead]

According to here, discrediting your opponent's sources is considered a logical fallacy.

My question is... how? I mean, if I say "well, the National Enquirer says..." to support my position, people are going to discredit it. But that's a fallacy? Are they just supposed to accept my using it to further my arguement?

[Tusculan]

Simply put: even a liar can sometimes tell the truth. Even though in normal life you would not rely on untrustworthy sources, pointing out the unreliability of the source is no decisive argument against your opponents position. He could still be right.

[mrsam]

Poisoning The Wells:

discrediting the sources used by your opponent. This is a variation of Ad Hominem.

Ad Hominem is not fallacious if the attack goes to the credibility of the argument. For instance, the argument may depend on a claim of expertise. Trial judges allow this category of attacks.

[BaldTaco]

Tusculan is right. It's kind of like Appeal to Authority. It's a good inductive argument, but not deductive. That is, these arguments don't prove the case absolutely, but they certainly do bolster it.

[ultrafilter]

It's not a fallacy to say that information from the National Enquirer is probably not right, and to want independent confirmation. It is a fallacy to say that something is wrong because it was printed in the National Enquirer.

[MC Master of Ceremonies]

Originally posted by Speaker for the Dead
According to here, discrediting your opponent's sources is considered a logical fallacy.

My question is... how? I mean, if I say "well, the National Enquirer says..." to support my position, people are going to discredit it. But that's a fallacy? Are they just supposed to accept my using it to further my arguement?

This is the link that I posted a few months ago for someone isn't it?

IIRC it says also that just because an argument falls into one of these catergories doesn't necessarily make it fallacious.

[moriah]

Even the devil can sometimes tell the truth.

[Walton Firm]

I think it's important to distinguish between statements of fact versus logical arguments.

If someone cites The Onion to support your assertion that the Harry Potter books are driving children into the arms of witch cults, pointing out that The Onion is a satirical magazine is not fallacious.

On the other hand, if someone cites the National Rifle Organization as saying that "gun control laws only affect honest citizens because criminals, by definition, do not obey the law anyway", pointing out that the NRA is not an objective source does not invalidate the argument, because it stands on its own merit and therefore does not depend on the trustworthiness of the source.

[slipster]

To expand--or restate--what Martin Wolf has said, it is not fallacious to criticize a source of information when arguing that you should not rely solely on that source. It is fallacious to argue that because you can criticize a source of information it therefore follows that what it says is always false.