A Simple Introduction to Logical Fallacies

This article is an excerpt from my book The Decision-Making Blueprint.

Aristotle once described humans as “the rational animal.” He claimed that rationality is our “distinguishing characteristic,” the ability that sets us apart from all other animals.

Unlike other creatures, humans have the capacity to apply logic, establish facts, and make sense of things.

We do that by reason, and the process of doing so is called reasoning.

But just because we’re capable of these things doesn’t mean we’re good at them.

Logical Fallacies

The brain is vulnerable to so called cognitive biases—thinking errors in the way we process information.

On top of that, the brain doesn’t appear to have evolved for precise logic. There are many reasoning traps that our minds fall into. These are called logical fallacies: “the modes in which, by neglecting the rules of logic, we often fall into erroneous reasoning.”1 Or, put simply: errors in reasoning.

Logical fallacies are like tricks or illusions of thought and, as such, they can often be difficult to spot. As an example, consider the organ donor study below2.

Swedish Organ Donors

This graph shows the percentage of people across several European countries who are willing to donate their organs after they die. Note that Sweden, for whatever reason, has a slightly lower consent rate than the other countries on the right.

And now, let’s imagine that you’re in charge of increasing that number. How would you go about that?

One thing you could do is include a note on the organ donor form that says something like: “The vast majority of Swedes donate their organs.”

That’s a very persuasive statement that would probably convince a lot more people to donate. But, looking at it logically, it really shouldn’t.

“Everybody’s Doing It”

Donating your organs might very well be the right thing to do. But the fact that many people donate has nothing to do with it.

Just because something is popular, that doesn’t make it the right decision. As we all know, a lot of people have been wrong about a lot of stuff a lot of times.

So if someone reads that “the vast majority of Swedes donates their organs” and chooses to donate based solely on that fact, they’ve fallen for a logical fallacy known as appeal to popularity.

And that’s completely understandable. If something is popular, our common sense tells us it must be also be good, true, or valid.

But that’s not the case, and if we don’t pay attention to logical pitfalls like this, they will cloud our judgment and create poor decisions.

Don’t Be Fooled

By becoming aware of logical fallacies, you can identify and call out poor reasoning. You’ll be able to examine information critically and adjust your decisions accordingly.

And that’s an important skill, especially in a society where politicians, media, and marketers pray on logical fallacies to influence your thoughts, feelings, and actions.

So, in the articles below, we’ll look at the most common logical fallacies, and how you can expose and prevent them. Enjoy! 🙂


  1. Elementary Lessons in Logic: Deductive and Inductive by by W. Stanley Jevons
  2. Do defaults save lives?

Logical Fallacies Articles