Logical Fallacies

I. Definition and Key Ideas

“It’s a fallacy that eggs are bad for you”; you’ve probably heard the word fallacy used this way – to refer to false beliefs.  Logical fallacies, or just “fallacies,” in philosophy, are not false beliefs; to oversimplify, they are logical errors in argumentation, reasoning, explanation, rhetoric, or debate. But their precise definition is elusive and controversial; we’ll come back to that.

Fallacies are an important aspect of our lives.  Without being able to identify bad reasoning, humans can be sold all kinds of harmful beliefs, with dreadful consequences.  Politics, advertising, and human manipulation in general are full of fallacies; personal and societal health might depend on being able to spot them.


If we elect leaders whose policies are founded on fallacious arguments (logical errors), the consequences could include economic recession, war, or environmental disaster. On an individual level, advertisers are constantly trying to persuade us to spend money on their products; you have to be critical of their claims (look for the fallacies) if you don’t want to waste your income.

On the other hand, logical fallacies are also an acceptable method of persuasion in most contexts outside of academia.  If you use logical fallacies to win arguments, probably no one but a teacher or philosopher will call you on it!

There are 100s of named fallacies now, from familiar ones like the false dilemma and red herring, to the obscure, such as the “if-by-whiskey” argument and “chronological snobbery” (judging a belief to be wrong because it was believed during the same era as something else that was wrong).


II. The Core Fallacies (per Irving Copi (1961)):

  1. The fallacy of equivocation: exploiting semantic ambiguity
  2. The fallacy of amphiboly: exploiting syntactic ambiguity

3 & 4. The fallacies of composition and division: attributing a property of the whole to one of its parts, or vice versa.

  1. The fallacy of begging the question
  2. The fallacy of the complex question: asking a question with an unfair assumption or accusation within it, such as “have you stopped beating your wife yet?”
  3. post hoc ergo propter hoc (after this, therefore because of this).
  4. The fallacy of ignoratio elenchi (irrelevant conclusion): making an irrelevant argument that is supposed to settle the argument in question.
  5. The ad verecundiam fallacy: the appeal to authority or expertise
  6. The fallacy ad populum: the appeal to popularity
  7. The fallacy of ad baculum: the appeal to threat
  8. The fallacy ad misericordiam: the appeal to sympathy
  9. The ad hominem fallacy: attacks the person instead of the topic being discussed
  10. The fallacy of faulty analogy: is A and B are alike in one aspect then they must be alike in other things.
  11. The fallacy of the slippery slope: the belief that a small action/idea can lead to a worse event and so on.


III. Types

Formal fallacies are errors in pure logic; they would be fallacious no matter the topic.  A formal fallacy for example is thinking that “If A then B” implies “If B then A.”  In other words, the fact that you don’t go to work when you’re sick, does not mean that if you’re not at work, it’s because you’re sick (maybe don’t explain that one to your boss).  The fact that this reasoning is wrong does not depend on what A and B are.  In practice, people don’t make a lot of formal fallacies.  Most of them are “informal.”

Informal fallacies: Most or all of the fallacies you’ve heard of are known as “informal fallacies”—not meaning that they are suitable for casual-dress affairs.  Informal fallacies are fallacious because of their content as well as, or instead of, their logical form. For example, there’s nothing wrong with the logical form of a “false dilemma” (a kind of fallacy) or an “appeal to authority” (another fallacy); it’s their specific assumptions that make them fallacious.


IV. Controversies

The definition of “fallacy” and the criteria for identifying one in practice are the biggest controversies in the theory of fallacies.  For example, you can’t define a fallacy as an argument that leads to false conclusions; a fallacious argument does not necessarily imply a false conclusion; in fact, that’s called “the fallacy fallacy”!  For example, all known arguments claiming to prove that God exists are fallacious, but that doesn’t mean she doesn’t exist.  It doesn’t mean she does either.

Theorists generally use the working definition that fallacies are “arguments which appear valid but are not.”  But even this “appearance condition” doesn’t really work, because then, whether something is a fallacy or not depends on the person hearing the argument; if I see through your fallacies immediately, then they’re not fallacies, according to that definition.

Recent decades have seen more original proposals about the nature of “fallacies.”  For example, that they are not essentially failures of logic, but pragmatic, rhetorical, or epistemic failures.  It’s an interesting discussion because it revolves around how one defines “good reasoning.”


V. Famous Quotes

Quotation #1:

“An expert is a person who avoids the small errors while sweeping on to the grand fallacy.” — Steven Weinberg

A perfect example of Weinberg’s statement is the way astronomers, for 1000s of years, recorded the precise movements of the planets in the sky, while still concluding that they revolved around the Earth. It is a fallacy to trust an expert; knowledge does not guarantee solid reasoning. So, fallacy can infect arguments of earth-shattering importance at least as easily as smaller issues.

Quotation #2:

 “I live by fallacy. ‘If I get enough nice Ikea furniture, I’ll be a grown-up.’ Then I catch myself. Or, ‘If I get off by myself, away from the stress of modern life, I’ll be OK.’ Then I catch myself.” — Chuck Palahniuk

And who doesn’t “live by fallacy” according to Palahniuk’s description? Fallacious rationalization may be one of humanity’s most pervasive characteristics; we are all masters at pulling the wool over our own eyes, as another iconoclastic writer, Robert Anton Wilson, described it.  Learning to recognize fallacies can make you more perceptive and give you self-knowledge.

VI.  Fallacies in Pop Culture

Example #1: Advertising and television

Most advertising, even if just a series of images, implies fallacies.  The purpose of advertising is to get you to buy things you don’t really need, so it relies on deception (fallacies) to persuade you.  For example, advertisements often imply through images that if you use their product, you will be better looking, happier, and more successful.  Since products have very little relevance to our happiness and success (which depend mainly on relationships and hard work), and since we are probably better off saving our money, these arguments are almost always fallacious. But advertisers may use many other fallacies, as shown in this video.

Example #2: The core fallacy of pop culture: ad populum

One of the core fallacies lies at the very heart of popular culture; ad populum is reasoning that something is correct because it’s popular.  The fallaciousness of this reasoning is obvious.  Popular opinion has often been dead wrong; for example, cocaine was once popularly believed to be good for your health. Smoking too.  And, although judgements of artistic quality cannot ultimately be right or wrong, it is still fallacious to believe that a popular artist must be a good artist.


VII. History

The oldest recognized discussion of fallacies is Aristotle’s Sophistical Refutations, an essay that deals in excruciating detail with techniques of proof and refutation.  He identified 13 fallacy-types, which are still among the most well-known, such as the ones we call equivocation (confusing two different meanings of a word) and begging the question (assuming what you claim to be proving).   Following Aristotle there was a pause in in the evolution of logic for about 2,000 years except for some activity in the late Middle Ages following up on Aristotle.

Then, around 1600, arrived the Age of Reason, with many philosophers, such as Francis Bacon, John Stuart Mill, and John Locke, writing about the importance of sound reasoning and about fallacious arguments—although they didn’t necessarily use the word ‘fallacy.’  John Locke’s contribution is especially noteworthy because he described several types of argumentation that have become among the best-known fallacies today.  For example, most people know that the ad hominem fallacy means to attack a person instead of their argument. When Locke named it, he was referring to something slightly different — attacking a person’s argument on the basis that it is inconsistent, either internally, or inconsistent with other things they’ve done or said—which is a commonly accepted argumentative technique today, at least in presidential debates!

After Locke, the next great landmark in the history of fallacies came in 1961.  Irving Copi published a classification of fallacies, in his Introduction to Logic, which remains acceptable to philosophers today, as a manageable list of major fallacy types (see section five).  Copi’s publication also sparked a new period of questioning and new perspectives in fallacy theory, which continues today.

VIII. What Makes a Fallacy… a Fallacy?

Though we learn to call them “logical fallacies” in school, in fact, philosophers have been unable to agree on what exactly makes a fallacy a fallacy; many fallacies include logical errors, but most of them cannot be called “fallacies” without reference to their specific content.


A common fallacy is post hoc ergo propter hoc – to infer that if B follows A, in time, then A caused B.  But in many cases, this is not an error.  It depends on whether you’re talking about, for example, a flame appearing after you strike a match or unemployment going down after a new president enters office.  In the first case, it’s solid reasoning; in the second, it’s fallacious.

Philosophers also debate whether teaching fallacies improves people’s reasoning abilities.  There are an infinite number of fallacious arguments.  Perhaps it would be wiser just to teach good reasoning?! However, brain science supports the idea that having a label for something makes it easier for us to remember and think about. And since we are constantly being hammered with fallacious, misleading arguments in life, it is probably worth anyone’s time to practice identifying them.  At the very least, you’ll raise the level of debate among your acquaintances during the next presidential election!


All logical fallacies . . .





You can tell whether any argument is fallacious by . . .





An “informal fallacy” is . . .





An example of post hoc ergo propter hoc is . . .





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