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Ad Hominem

Entry 1479, on 2012-12-18 at 19:51:35 (Rating 3, Skepticism)

Looking back through my old blog entries I have found a post where I said that I would do a series on logical fallacies and how people could use them to improve their debating and thinking skills. I have only covered one so far, special pleading, and a commenter noted that he would await further entries so, here goes...

The logical fallacy I want to cover this time is the "ad hominem". This is an attack against a person rather than a point if view or argument. The definition from the encyclopedia of philosophy is: "Your reasoning contains this fallacy if you make an irrelevant attack on the arguer and suggest that this attack undermines the argument itself."

It's interesting to note one word there which is sometimes left out, that is "irrelevant". I will come back to this point later.

Ad hominem fallacies are very common and it's difficult to avoid them entirely. They occur when an argument is rejected because of a disagreement with the person making it. Sometimes the rejection is completely unsupported, and on some occasions it is partly appropriate, but in many cases it has little relevance (in which case it would be a clear case of the ad hominem fallacy).

Here's an example: a global warming denier might say that he doesn't believe in the phenomenon because the people who support it are scientists who are all to the left politically making them unreliable.

This is an ad hominem attack because scientists occupy a spectrum of political views and even if they were all to the left it would make no difference to the facts they are presenting. Those facts can be independently checked and are open to peer review. Any argument of this sort should be either rejected, or at least treated with great suspicion because it really can't be taken seriously.

Here's a less clear example: the movie "An Inconvenient Truth" cannot be taken seriously because it's about Al Gore who has a political agenda.

There are inaccuracies in this movie and Al Gore is a political activist for action on global warming, but that doesn't mean the many facts and accurate reports in the movie can be ignored. It does mean it doesn't have as much credibility as it would have if it was about an independent expert discussing the same subject but it should still be considered and fact checked. When that is done the greatest part of the movie is found to be relevant and accurate.

Finally there is this: I always ignore my neighbour who thinks climate change is just a vast conspiracy. He works for BP and is a member of the local libertarian party. He also supported many other pro-industry causes in the past such as contributing to the denial of cigarettes causing cancer and aerosols causing the ozone hole.

This is an attack against the neighbour as opposed to his ideas but I think it is largely justified. Because the criticisms of the person are relevant to the point under discussion this isn't an ad hominem.

First, the neighbour has produced no facts at all to support his denial of climate change: he has simply stated that he thinks it's a conspiracy. It's possible that it actually is one but without any verifiable evidence that contention is useless. He also has a very clear reason to reject climate change whatever the facts may be because he works in an industry which would be affected by any action taken and belongs to a political party with a dogmatic view against it. Finally he has a history of rejecting similar phenomena which are now clearly accepted as true even by most of the people who initially rejected them.

Clearly all debating should involve examination of the facts rather than the character of the people involved but there are some people who present such weak arguments and have such clear biases that it's sometimes more practical just to initially assume their argument is baseless. There are also a few "serial offenders" who make the same mistakes, or present the same misinformation, over and over. For example there are people involved in climate denial now who also worked for the tobacco companies in propaganda campaigns against the dangers of smoking. I think it is OK to reject these people's arguments with little further thought.

In a perfect world - one where we had plenty of time to look at everyone's opinion - we could look at the claimed facts behind everyone's opinion and accept or reject them based on that. But the reality is that sometimes that just isn't possible, and an attack against the person is acceptable without it being labelled as an ad hominem.

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