If you’re like me, you probably do quite a lot of net surfing, just looking for new science stories or something interesting to read. But I hope that you think critically about what you’re reading. Not all websites are created equal, and the material you find may contain one or more logical fallacies. Check them out – not least because learning to recognise them will help you to avoid using the same fallacies in your own writing.
You may find examples of what are called ‘ad hominem’ fallacies, where the author casts a slur on someone else, rather than discussing their work. (This is quite common in creationism/evolution debates.)
Another is what’s called the ‘ad populum’ fallacy – everyone thinks so, so it must be true. Well… let’s think about this one. A 2006 Gallup poll found that 53% of US citizens believed that the Earth is only 6000 years old – but just because a majority think this so, doesn’t make it a reality!
And there’s the use of anecdote to make your point. Anecdotes, and testimonials from happy customers, are often used as selling points. But these are personal statements; they don’t carry the weight of scientific evidence.
On a related front, watch out for the ‘appeal to authority’ approach: Dr Bloggs says so, so it must be true. But what are Dr Bloggs’ credentials? Is this a field in which she’s an expert? What is the basis for her statement – is there a citation that you can check out? Checking citations may also let you recognise the use of quote-mining, where someone takes a statement out of context and uses it to support an argument.
You may encounter the use of ‘false dilemma’: your choice is reduced to this, or that. An example would be recent attempts to persuade us that intelligent design is the correct explanation for the diversity of life on Earth, by putting forward evidence that evolutionary theory is incorrect. This argument was firmly quashed by Judge John Jones (in the Kitzmiller et al. vs Dover School Board case) who stated that “Intelligent Design is at bottom premised upon [the] false dichotomy… that to the extent evolutionary theory is discredited, ID is confirmed”.
You may also come across the use of ridicule and emotion to downplay the importance of someone else’s view, or add weight to an opinion. That last one is easy to slip into yourself when you’re writing essays – using words like ‘horrendous’ or ‘awful’ to describe a process or an outcome, for example. Why not just let the facts, and your argument, speak for themselves?
Like other skills involved in critical thinking, learning to spot and avoid logical fallacies is a learned skill. You’ll have to work at it – but it’ll pay off in the long run.