Do we really have a fast mind and a slow mind?

Psychologists often describe thinking as two modes rather than two literal minds: a fast, automatic, intuitive one, nicknamed System 1, and a slower, effortful, step-by-step one, System 2. It's a useful map, but the latest research says the border between them is blurrier than the famous version suggests.

Try this. A bat and a ball cost $1.10 in total, and the bat costs $1.00 more than the ball. How much is the ball? The answer that leaps to mind is 10 cents. It's wrong: then the bat would cost $1.10 and the pair $1.20. The ball costs 5 cents. Getting there means noticing that your first answer is off, and that noticing is the whole point of the test.

The psychologist Daniel Kahneman, who won the Nobel prize in economics for his work on judgment and decision-making, popularised the two systems in his 2011 bestseller Thinking, Fast and Slow. System 1 is quick, emotional and runs on habit. System 2 has limited capacity because it uses working memory, so it's slow.

Here's the nuance. Fast doesn't always mean System 1, since practice can speed up careful reasoning, and both modes can be right or wrong. Many researchers prefer a single continuum to two boxes. And some studies in Kahneman's book didn't replicate; he admitted, "I placed too much faith in underpowered studies." Intuition, meanwhile, is pretty good where we get lots of quick, reliable feedback, like reading people we know well.