Madsen Pirie

A short guide to winning arguments

Madsen Pirie says that logic and a few Latin terms can help you destroy any challenger in intellectual confrontation

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When I taught logic at an American university, the chief problem was to entice students to take the course. The smorgasbord approach they used to build a degree meant that students wanted things which might be useful to them, or ones they might be good at. Logic, alas, was perceived as neither, and classes were largely made up of very bright students who were not afraid of it and who thought it might be fun.

It would be difficult to show that it is a valuable life skill, given the remarkable number of successful people who happily get by without it. Many high-achieving executives, respected media commentators and prominent politicians do not seem to be held back by a lack of logical fluency, while many who are precise with their words and arguments are neither successful nor popular; nor, indeed, are they rich.

The students were correct about the fun side of it, though. My staff colleagues used to demand a warning when the part of the course devoted to logical fallacies began. Students would point to alleged errors committed by professors and lecturers in other courses, giving impressive-sounding names to the fallacies they claimed to have spotted.

Does it win arguments, though? Yes, it can. If the cracked steps in an adversary’s chain of reasoning can be identified, you might not change their mind, but you might undermine their case to onlookers. You might also learn how to avoid gaps in your own arguments.

Some suggest, for example, that we should lower the speed limit on motorways to 60 mph on the grounds that it would save lives. One might dispute this, but surely it isn’t a fallacy? Yes it is. It is a runaway train. We might indeed save lives by lowering the limit to 60 mph, but if saving lives is our motive, we’d save even more by lowering it to 50 mph, and more still at 40 mph. The train doesn’t stop at 60 unless extra arguments are added, otherwise it goes on until we save the maximum number of lives, with a speed limit of 0 mph.

A speed limit represents a compromise between the need to reach places within acceptable times, and the risk of death or injury which high speeds incur. Currently, it has settled on 70 mph. To argue successfully against 60 mph, you need only ask why that figure is better than other ones. Any reduction might well save lives, but why that one?

England’s national fallacy is probably the argumentum ad temperantiam, which is the supposition that a moderate middle course must be the superior option. A distaste for extremism has ingrained in the English a preference for standing in the middle of every alternative, and thus reaching only halfway to accuracy and virtue. If you see someone in a pub claiming that two plus two equals four, against another who says they equal six, just walk over and suggest that five is probably about right. Every Englishman in the pub will nod sagely in agreement with your moderation. Nonetheless, sometimes one of the extremes may be correct; there is no link between moderation and accuracy.

If the English like the temperantiam, the environmentalists like apriorism. Some people get horses and carts the wrong way round. Normally when we see what the facts are, we either retain or modify the theories which predicted them. To give undue primacy to the theories is to venture into the territory of apriorism. It is quite OK if the warmest winter on record is taken as proof of man-made global warming. Even the coldest winter can be taken as evidence if you alter the name to ‘climate change’. But when an unusually wet winter is taken as proof, and the same is true of a very dry one, the facts cease to bear on the theory. This is the time to ask what kind of weather would count against the theory. If no conceivable outcome would do that, then the charge of apriorism sticks.

People often find it easier to refute a fake extreme opponent than a more cautious real one, so they knock down the straw man instead. They attack those who say that all old people should be kept off the roads, since these (non-existent) people are easier to defeat than those calling for an extra driving test at the age of 75. They try poisoning the well by suggesting that only a lunatic would disagree with them, waiting for the lunatics in question to identify themselves by their disagreement.

It is actually worth the trouble to identify the invalid forms of argument, and to learn their names. Not only can you then avoid them yourself; you can also identify them in opponents. If you call your opponent’s errors by their Latin names, you can make it look as though he or she is suffering from a rare tropical disease.

A favourite in daily use is called cum hoc ergo propter hoc. It is the supposition that events which occur at the same time must be causally connected. Thatcherism can be linked with rising crime, increased alcohol consumption, greater popularity of country and western music, and just about anything that happened in the 1980s. To use this yourself in argument, all you have to do is ask sarcastically if it was just a coincidence that the one event accompanied the other. When you hear others using it, though, just ask them to show you the connection.

A common, but cracked, argument uses initial assertions to prove something which contradicts them. Everything must have a beginning (or a cause or a purpose), they say, and then go on to deduce from this that there must be something which didn’t have a beginning (or a cause or a purpose). It’s wrong, but it’s reassuring, which is why it lasts.

Unsound arguments might be heard occasionally in pubs, but in Parliament they feature every day. The tu quoque supposes that your criticism can be ignored because of something you once did yourself. This allows Gordon Brown to reel off endless statistics about how bad things were under the Tories, thereby excusing himself from making them worse.

The British are reported to be gambling in record numbers, so it is likely that we are all comforting ourselves with the gambler’s fallacy. ‘Heads have come up five in a row, surely the odds must now be in favour of tails?’ (Wrong.) In fact, a professional gambler would probably bet on heads again, suspecting a crooked coin. The rest of us suppose that since we have lost thus far, surely our luck must change? Alas, no. It is more likely true that a pattern of foolish behaviour has begun to emerge. When you listen to Lord Hattersley and think, ‘Surely no one can be wrong all the time?’, do remember that it isn’t true.

How to Win Every Argument: the Use and Abuse of Logic by Dr Madsen Pirie is published this week by Continuum.