Why Logical Fallacies Work
History is full of brilliant minds who believed false things and defended absurd ideas. Isaac Newton spent decades trying to create the philosopher’s stone. Thomas Edison championed radioactive products as remedies for various ailments. Steve Jobs skipped bathing in the conviction that his vegan diet could cleanse his body of mucus and toxins.
The problem is not that intelligent people cannot think.
It is that they are human.
We all have hopes, fears, loyalties, ambitions, prejudices, and desires. We are naturally drawn to arguments that flatter our opinions, excuse our behaviour, or confirm our suspicions.
More than two thousand years ago, the ancient Greeks began studying arguments that were unsound and yet persuasive, calling them fallacies.
Learning to recognise them remains one of philosophy’s most practical lessons. But more interesting than what they are is how they work.
Why Bad Arguments Persuade Us
Most fallacies succeed not because they overwhelm our intelligence, but because they appeal to our human nature and frailties.
We are more receptive to arguments that confirm what we already believe than to those that ask us to change our minds. We welcome arguments that flatter our side, condemn our opponents, simplify a complicated world, or promise certainty where none exists.
Reason is less often an impartial judge than a disingenuous lawyer, excelling at defending conclusions that we reached for wholly other reasons.
And, sadly, the brighter the mind, the more elaborate—and persuasive—its rationalisations.
From Rhetoric to Logic
The study of fallacies emerged in ancient Greece as a branch of rhetoric, the art and science of persuasive speaking.
Following the reforms of Cleisthenes in 508 BCE, Athens became a radically participatory democracy. Citizens served as jurors, debated laws, and competed for influence not with swords but with words.
Sophists such as Gorgias, Protagoras, and Hippias enriched themselves by teaching this new art of persuasion. Gorgias was not merely a teacher of rhetoric, but a performer, master of verbal display, and intellectual celebrity. According to tradition, when he appeared in the theatre at Athens, he would invite the audience: “Come, propose me a theme.” He took pride in his ability to speak on any subject and defend even the most improbable of positions.
For Plato, this represented a profound problem. It had been by bad arguments that his teacher, Socrates, had been put to death. If persuasive speech could triumph over truth, what hope could there be for philosophy?
Plato’s pupil Aristotle sought to address these concerns by laying the foundations of logic.
If rhetoric explains how people are persuaded, logic asks when they ought to be.
Formal and Informal Fallacies
Logic distinguishes two broad kinds of fallacy: formal and informal.
A fallacy is a defect in an argument, whether accidental or deliberate.
Formal fallacies arise from the structure of an argument.
If I have the flu, then I have a fever.
I have a fever.
Therefore, I have the flu.
The conclusion, of course, does not follow, since I may have any number of other pyrogenic (fever-inducing) illnesses.
This formal fallacy is known as affirming the consequent.
Far more common are informal fallacies, whose weakness lies not in their logical form but in their content.
These are the fallacies that fill newspaper columns, political debates, boardrooms, dinner tables, and social media.
We Prefer People to Arguments
The easiest way to answer an argument is often not to answer it at all.
Instead, attack the person making it.
This is the ad hominem fallacy.
Closely related are the genetic fallacy, which judges an argument by its source, and the appeal to hypocrisy (tu quoque), which dismisses an argument because its author fails to live by it.
None addresses the argument itself.
They succeed because judging people is easier than judging ideas.
A striking example of the genetic fallacy came during the 2016 Brexit referendum. On 3 June 2016, the then Lord Chancellor, Michael Gove, declared: ‘The people in this country have had enough of experts…’
We Prefer Easy Victories
Some arguments are difficult to refute.
It is then much easier to invent a weaker one.
A straw man caricatures an opponent’s position before knocking it down.
Closely related is the red herring, which changes the subject altogether.
Neither brings us closer to the truth, but both bring us closer to victory.
Some regard straw man as a form of red herring, since both serve to deflect. ‘Red herring’ takes its name from the custom of using stinky smoked herring to throw dogs off a trail. Think of it as a form of pre-Internet trolling.
For example:
—Critical appraisal of the new Bordeaux vintage would be more objective and meaningful if the wines could be tasted blind.
—Just Bordeaux?
We Prefer Agreement
Human beings are social animals.
This makes us especially vulnerable to social arguments.
An appeal to popularity asks us to believe something because many other people believe it.
An argument to moderation assures us that the middle position must be right.
A false dilemma presents only two options when reality usually offers many more.
These fallacies appeal to our desire for belonging, certainty, and simplicity.
False dilemma is often a veiled attempt to force a Hobson’s choice of ‘take it or leave it’. For example, Theresa May insisted: ‘It’s my deal or no deal.’ At times, she expanded this into a false trilemma: ‘It’s my deal, no deal, or no Brexit at all.’
We Prefer Simple Stories
The human mind delights in finding patterns—so much so that it finds them where none exist.
Cum hoc ergo propter hoc (‘with this, therefore because of this’) mistakes correlation for causation.
The gambler’s fallacy imagines that independent events, like a throw of dice, somehow remember what came before.
Both satisfy our hunger for neat explanations in a messy world.
Cum hoc ergo propter hoc is also known as the Chanticleer fallacy after the fictional rooster who believed that his crowing made the sun rise. I prefer to think of it as the scientist’s fallacy.
We Prefer Being Right
Perhaps the most bone-headed fallacy of all is begging the question.
Instead of proving a conclusion, it quietly assumes it.
For example, the argument that opposes same-sex marriage on the grounds that marriage is the union between a man and a woman is no more substantial than ‘I’m right because I’m right.’
Circular arguments persuade because they begin where we already stand.
The Discipline of Thinking Clearly
This article may have seemed to be about reasoning.
It has really been about self-deception.
Logical fallacies endure because they satisfy our desires more readily than they satisfy the demands of reason.
We rarely believe bad arguments because we cannot think.
More often, we believe them because they tell us what we wanted to hear.
Learning to recognise fallacies in others is useful.
Learning to recognise them in ourselves is the beginning of self-knowledge.
Continue Exploring
If you enjoyed this introduction to logical fallacies, you’ll find many more practical lessons on reasoning and rhetoric in How to Think Like Plato and Speak Like Cicero.
To explore the forces that so often lead us astray, see Hide and Seek: The Psychology of Self-Deception.
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