Logical fallacies

Logical fallacies and other failures of reasoning are a stable feature of Usenet arguments, and even more prevalent on web forums. They represent failures, either deliberately or through ignorance, to apply proper scientific standards. Few are immune, I certainly am not - and for both the stated reasons. Identifying, and understanding the weaknesses of, fallacious arguments is important. Many of the fallacies are now widely used in the media. Every train crash is followed by &quot;no expense must be spared&quot; (misleading vividness), yet speed enforcement is denounced as unacceptable (slothful induction, special pleading). Wells are poisoned, fear, emotion and tradition appealed to, straw men slaughtered in their multitudes.

And there is no surprise that this should be so. A logical fallacy is not, after all, actually a lie, in the strictest sense, so is almost telling the truth nearly. And it is so much easier to demolish a straw man than a real one. People see what they want to see, and are easily seduced by what appears to be a logical argument which supports their own position. Which is where the observational studies went wrong, of course - it is much easier to believe what we want to believe than to challenge it in a rigorous way, not least because a robust challenge requires us to start from the premise: what if I am wrong?

This is a quick walk through the common forms of logical fallacy, culled in part from from Nizkor and from Stephen Downes' excellent index of logical fallacies. Both these sources are more extensive and give numerous examples. This is by way of a quick reference or spotter's guide. I have tried to keep the helmet content low, but there are some places where helmet examples sprung to mind. Please indulge me.

Remember, the fact that a logical fallacy exists in an argument does not prove that a claim is false; the claim remains unproven either way. And the inability of a person to argue a case without resorting to logical fallacies does not indicate that their case is necessarily wrong (although the longer it goes on stronger the inference becomes), just as the ability to avoid them does not make someone right. You have to go back to the sources, review the evidence and make up your own mind.