What are cognitive biases?

In my first post, I described epistemic and instrumental rationality. In this post we’re going to take a look at one of the greatest enemies of epistemic rationality: your own brain.


In all seriousness, a human brain does a lot of things right, but it also does a lot of things wrong. One of the ways your brain can do things wrong is called a cognitive bias. If you’ve spend some time around Less Wrong affiliated people, you’ve probably heard of the word “bias”, but what does it mean? In the following paragraphs I’ll attempt to explain what a cognitive bias is.

You can compare a cognitive biases with optical illusions.


You probably already seen this one, so you know all the lines are straight, but you can’t help but perceive them as crooked. A cognitive bias is similar, but instead of tricking the way you see, it tricks the way you think. Even if all the information you have is accurate, your brain can come to incorrect conclusions.

Here‘s an example of how your brain can be tricked:

It’s important that you note the first answer that comes to mind, you shouldn’t be spending time writing this down and working out the equation.

“A baseball bat and a baseball together cost $1.10. The bat costs one dollar more than the ball. How much does the ball cost?”

Just note the first answer that comes to mind.

There’s a good chance you thought $0.10. This is wrong. Feel free to work out why, or click the link if you want to know the correct answer.

And if you got it wrong: don’t feel bad, more than half of the people answering that question made the same mistake.

This is just one of the ways in which your brain can fool itself and the list of all the ways in which this sort of thing can happen is really, really long.

So really, you can’t trust your brain when looking at the world. This isn’t your fault however. Your brain isn’t equipped for all this. It’s the product of evolution, made so you can successfully hunt, gather and do tribal politics. It wasn’t made for solving ball-and-bat problems or looking at weird circles that seem to move. Those things just didn’t happen in the environment you were made for.

And really, a lot of biases are really just shortcuts your brain takes because a lot of the time there isn’t any problem in taking them. Nevertheless you need to be prepared for the times when taking the shortcuts is dangerous. There are people who know about biases and can and will exploit them to get ahead. There are problems you won’t be able to solve properly unless you overcome certain biases.

Which leads us to the good news. Most biases can be defeated or circumvented. It isn’t always easy, but by reading this far you’ve already taken the first step. Knowing about certain biases can be enough to get to more accurate beliefs for some people.

In the future, we will discuss specific biases and how to overcome them. If there’s a particular one you want to see discussed, feel free to let me know.