System 1 and System 2: How to Think Better

Imagine that I ask you, “What’s 2 + 2?”

You can’t help but think of the answer. The number “4” instantly pops into your head. If you’ve learned basic math, it’s impossible not to immediately think of the answer. This is the result of what scientists call reflexive brain.

Now, imagine that I instead ask you, “What’s 39 multiplied by 26?”

Most likely, your brain goes blank. It doesn’t have an instant answer. Unless you’re a math wizard, you have to go through the tedious process of calculating it. You have to use what is known as your reflective brain.

System 1 and System 2

In his book Thinking Fast and Slow1, Daniel Kahneman termed these two modes of thought as System 1 (reflexive) and System 2 (reflective):

“System 1 operates automatically and quickly, with little or no effort and no sense of voluntary control. System 2 allocates attention to the effortful mental activities that demand it, including complex computations.”

In other words, System 1 is intuitive, and System 2 is deliberate. These two modes of thought complement each other, and they’re both active whenever we’re awake.

System 1 is the first layer of thinking that our brains delegate problems to. System 2 only comes into the picture when System 1 doesn’t have an answer.

That arrangement usually works pretty well because System 1 is generally good at what it does. It’s not perfect, however, and there are many situations where decisions should ideally be delegated to System 2, but System 1 makes them anyway.

As an example, consider the simple math problem below. Don’t try to solve it—just observe the intuitive answer that comes to mind.

The Bat and the Ball

The total cost of a baseball bat and ball is $1.10. The cost of the bat is $1.00 more than the ball. How much does the ball cost?

System 1 will tell you that the ball costs 10 cents, which is the wrong answer. If you do the math using System 2, you’ll realize that the right answer is 5 cents (and $1.05 for the bat).

This example illustrates the problem with System 1. While fast and effortless, it’s also prone to mistakes. In fact, the sloppiness of System 1 is what creates the cognitive biases and logical fallacies I’ve written about previously.

How to Use System 1 and System 2

Despite its flaws, you shouldn’t try to turn off System 1 and operate solely in System 2. According to Kahneman, that wouldn’t be possible nor desirable:

“Constantly questioning our own thinking would be impossibly tedious, and System 2 is much too slow and inefficient to serve as a substitute for System 1 in making routine decisions. The best we can do is a compromise: learn to recognize situations in which mistakes are likely and try harder to avoid significant mistakes when the stakes are high.”

When you’re making mundane and inconsequential decisions, let System 1 run. It’s okay that it’s wrong now and again because it saves valuable mental energy and reduces decision fatigue.

But when you’re about to make an important decision, switch to System 2. Deliberately slow down, take your time, and use mental models to reach the best decision possible.

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


  1. Thinking, Fast and Slow by Daniel Kahneman

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