logical fallacies


“You can’t prove there are no aliens on Jupiter, so I conclude there are.”

Ladies and gentlemen, let me introduce you to the appeal to ignorance fallacy, one of the many logical fallacies that don’t hold firm under careful inspection.

Logical fallacies are arguments that rely on faulty logic, undermining your authority as a writer and speaker. While some fallacies may sound convincing at first, especially when they appeal to emotions – “if you fail this exam, who’s to say you won’t fail another one, eventually dropping out of school and turning into a massive disappointment” (slippery slope fallacy) – but one closer look is enough to make them fall apart – “if you fail this exam, you can simply resit.”

These faults in reasoning are something you should strive to avoid in your writing, be it academic writing (where sound arguments are especially important) or fiction writing (where world-building and plotting should rely on logic and common sense to a large degree).

But first…

Where Do Logical Fallacies Come From?

The word fallacy originates from the Latin fallacia, which means “trick” or “deceit.” The concept goes as far back as ancient Greece when the philosopher Aristoteles wrote Sophistical Refutations, a work comprising thirteen different fallacies and their classifications.

Aristoteles divided logical fallacies into two major categories:

  • Verbal – an argument is faulty due to an ambiguous use of words
  • Material – an argument is faulty due to illogical contents

Throughout the centuries, logical fallacies have found their place in academia and have been classified further, helping us navigate the world of critical thinking.

RELATED READ: 5 Tips for Writing That Will Make You a Better Writer

Logical Fallacies: Categorization & Examples

Based on the current categorization, logical fallacies are either formal or informal. Formal fallacies pertain to the very structure of your argument:

Premise A: All potatoes are vegetables.
Premise B: All cucumbers are vegetables.
Conclusion: All potatoes are cucumbers.

As you can see, the deduction process here is wrong. While potatoes and cucumbers are both vegetables, this does not make them the same.

Informal fallacies, on the other hand, are all about the content of what you say. They are divided into five categories:

  • Linguistic fallacies
  • Fallacies of omission
  • Fallacies of intrusion
  • Fallacies involving built-in assumptions
  • Casual fallacies

According to Jacob E. Van Vleet, professor of philosophy and author of Informal Logical Fallacies: A Brief Guide, learning more about informal fallacies is an excellent way to increase your analytical skills, be able to detect poor arguments, and challenge the world around you.
What’s more, improved critical thinking will inevitably make you a better writer.

Ready? Let’s go!

Linguistic Fallacies

Linguistic fallacies relate to faulty or ambiguous language. While there are plenty of linguistic fallacies to decipher, here are two examples:

The fallacy of division (or whole-to-part fallacy) says that if the whole group has a certain characteristic, it must mean that every single part/member of that group possesses it as well.

Example: “The theatre in our town is excellent. Therefore, every single performance in this theatre is excellent.”

The fallacy of equivocation (or the double-meaning fallacy) occurs when one-word containing multiple meanings is used vaguely in an argument.

Example: “Man has walked on the moon. Women are not men, therefore, women have not walked on the moon.”

In this case, “man” is first used in relation to humankind, after which it’s associated with the male sex only.

Fallacies of Omission

Fallacies of omission leave out certain components of reality on purpose, misleading us or giving us the impression there are fewer possibilities to choose from. For instance:

The fallacy of bifurcation (or the black-and-white fallacy) makes it appear as though there are only two choices. If x is false, it must mean that y is true.

Example: “You’re either completely evil, or completely good. Since you’re not completely evil, it must mean you’re completely good.”

Argumentum ad ignorantiam fallacy (the appeal to ignorance) uses the lack of proof to support its assertions.

Example: “There is no proof that God does not exist. Therefore, God exists.”

Fallacies of Intrusion

Contrary to fallacies of omission, fallacies of intrusion add certain elements to the argument in order to convince the listener. These additions are often irrelevant or emotionally based.

Argumentum ad hominem fallacy happens when you verbally attack a person in order to undermine their argument. Slander is often used, but critiquing the person’s circumstances (saying they may have selfish motives and want to climb up the social hierarchy, for instance) also applies.

Example: “You shouldn’t listen to what Lea says because she’s stupid. Plus, she only says all this because she wants to be the best in our class.”

Argumentum ad verecundiam fallacy relies on false authority to support one’s statements.

Example: “I know this type of diet will help me lose ten kilograms in one month because my favourite celebrity said so.”

RELATED READ: Metaphor vs. Personification

Fallacies with Built-in Assumptions

As the name suggests, this type of reasoning relies on one’s assumptions to create an argument. However, the assumptions themselves don’t hold enough weight to support the argument’s logic.

Is-ought fallacy moves from a descriptive statement “is” to a prescriptive statement “ought” without sufficient proof.

Example: “Humans have evolved to fight for survival. Therefore, we ought to always fight for survival.”

Appeal to human nature fallacy occurs when you use the idea of human nature to support your statements without clearly defining what human nature is.

Example: “It’s human nature to have enemies. Therefore, I did nothing wrong when I fought that man who supports a different football team.”

Casual Fallacies

Casual fallacies lie in the misunderstanding of cause and effect. For instance, if two things correlate, it does not necessarily mean one causes the other – but casual fallacies state precisely that.

Post hoc ergo propter hoc fallacy translates from Latin as “after this, therefore because of this.” This is the assumption that because event B happened after event A, it must mean event A caused event B.

Example: “The price of ice cream skyrocketed after the new president had been elected. Therefore, the new president increased the price of ice cream.”

The slippery slope fallacy says that if one specific event happens, it will inevitably lead to a chain of disastrous events. This often evokes fear in listeners.

Example: “If you study English Literature, you’ll never find a job, will live a miserable life, and will become a spinster with eleven cats because no one will want to marry you.”


And there you have it! You now know what logical fallacies are, where they come from, how they are classified, and what some of the most well-known fallacies state.

Next, make sure to avoid them in your writing, especially in academic essays. In order to create sound arguments, rely on objective facts, previous evidence-supported research, and logical deduction.

If in doubt, consult the First Editing Blog for further advice.

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