Fast Brain, Slow Brain: Why Your First Answer Is Usually the Lazy One

Try this: A bat and a ball together cost $1.10. The bat costs $1 more than the ball. How much does the ball cost? If “10 cents” jumped out at you, you are in good company, and you are wrong. The ball costs 5 cents. That quick, confident, wrong answer is your fast brain at work, and learning to catch it is one of the first skills of critical thinking. This article covers:

• Meeting your two modes of thinking
• Seeing why the fast brain takes shortcuts
• Spotting the traps it walks into
• Switching on your slow brain

Meeting your two modes of thinking

Psychologist Daniel Kahneman, who won a Nobel Prize for his research on judgment, argues that people have two ways of thinking:

• A logical mode, which is slow and deliberate
• An earlier, instinctive mode, which he sees as the root of most wrong decisions

Much of what you think is instinctive and hardwired, a legacy of ancestors whose survival depended on quick reactions.

Seeing why the fast brain takes shortcuts

Thinking is expensive. The human brain uses about 20 percent of an adult’s energy, and almost half of a child’s, so the body is programmed to avoid it where it can. Over thousands of years, people have developed mental shortcuts, called heuristics, for reaching decisions quickly. The brain also:

• Dislikes information gaps, so it jumps at the first answer that looks good
• Loves patterns and connections, which sometimes mislead

These habits are often efficient, but they can rush you to the wrong conclusion. The real problem is that fast thinking often solves the easy problem instead of the right one.

Spotting the traps it walks into

Two classic traps:

• The Linda Problem: Volunteers read about Linda, a bright philosophy graduate concerned with social justice. Asked which was more likely, “Linda is a bank teller” or “Linda is a bank teller and is active in the feminist movement,” 89 percent chose the second.
• Two things together can never be more likely than one of them alone.
• The stereotype beat the logic.
• Stereotypes over statistics: If two people on your street were robbed last year, you probably overestimate local crime, whatever the official figures say. Newspaper headlines distort your sense of risk in the same way.

Switching on your slow brain

Critical thinking is your insurance policy against these habits. In practice, that means:

• Pausing when an answer arrives suspiciously fast
• Checking the math instead of trusting the feeling
• Asking whether you are solving the problem actually in front of you
• Treating a vivid story with caution until you know the numbers behind it

Fast thinking is not the enemy. The trouble starts when it answers questions it was never built for, and knowing when to slow down is where critical thinking begins.

Ready to hone your critical thinking skills? Check out the Critical Thinking Skills For Dummies book or take the course.