The way we argue now

Public debate has grown with online media, but poor reasoning and weak arguments are everywhere. Before you go on that discussion board, read our guide to dodgy rhetoric

New light: The Thinker by Rodin. Photograph: E+/Getty

New light: The Thinker by Rodin. Photograph: E+/Getty

Sat, Aug 16, 2014, 01:00

Poor reasoning and weak arguments appear practically everywhere. Discussion and analysis, both in print and online, are all too often riddled with dubious reasoning. The more contentious the issue, the more extreme the flurry of dodgy claims it generates. Flawed logic is ubiquitous, ranging from genuine ignorance to odious dishonesty. It can all too easily derail constructive discussion and damage our ability to make sound decisions.

Here are some of the common reasoning flaws found in modern discourse, which are scuppering our ability to make good decisions.

Cause-and-effect fallacies 
Umbrellas are associated with rain but don’t cause it: the logic seems pretty clear, but such nuance is thrown to the wind in discussions about science, health and politics. It can be surprisingly hard to make a robust causal connection; there are usually so many confounding variables that it takes a carefully controlled analysis to work out the underlying relationship, if any.

This doesn’t seem to stop people making erroneous links and disproven connections, whether it be the assertion that vaccinations cause autism, fluoride causes Alzheimer’s or homosexuality causes Aids.

These are also examples of the reduction fallacy, an often misguided attempt to ascribe single causes to outcomes that are in reality complex interplays of many factors, such as some newspapers’ ongoing quest to divide the entirety of creation into a neat “causes cancer/cures cancer” dichotomy.

Causation fallacies are so versatile that they can be employed even without any evidence of correlation, just an asserted order of events. This related fallacy is “Post hoc ergo propter hoc” (“after this, therefore because of this”). This is used to brilliant comic effect by the parodic Church of the Flying Spaghetti Monster to assert that a drop in the number of global pirates since the 1800s has caused global warming.

It is possible to engage in the same fallacious reasoning in reverse, by denying the causative role of an agent that has been rigorously shown to cause a given effect. Sixty years ago the tobacco industry attempted to pour doubt on the emerging scientific consensus that smoking caused lung cancer.

Similarly, many people today deny the link between human activity and climate change, despite incontrovertible evidence.

Personal biases and motivated reasoning
Humans are social animals, and information from and the opinions of people around us tend to colour our own. Despite this, anecdotal assertions are perhaps the most common signs of a dubious argument.

Being casual observations rather than rigorous controlled tests, they usually fail to consider confounding factors or alternative explanations. A person who insists that homeopathy works for them, for example, may be unaware of other, more likely explanations – placebo effect, regression to mean, observer bias – which describe the same thing without requiring an ad-hoc rewriting of the laws of physics. Anecdotes are persistent and difficult to discount precisely because they are personal stories, far more engaging than dry scientific data.

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