Thinking, Fast and Slow

Daniel Kahneman uses fast, intuitive thought and slower, effortful thought to explain patterns in judgment. These are useful descriptions of mental processes, not two literal people or separate switches in the brain. The publisher's introduction and excerpt set out the distinction and the book's focus on uncertainty and confidence.

Try a base-rate check

Here is an original Nuxflo example. A volunteer group has 80 event helpers and 20 archivists. You meet someone who enjoys detailed lists. Is that person probably an archivist?

The description sounds relevant, but it leaves out an essential comparison: how common is that preference in each group? Suppose 40 of the 80 helpers and 15 of the 20 archivists enjoy detailed lists. Among people with that preference, 15 are archivists and 40 are helpers. The chance of being an archivist within this invented group is 15 out of 55, about 27%. A trait can be more common among archivists and still describe more helpers overall.

What to write beside a persuasive story

Make three notes: the starting proportions, the new evidence, and how often that evidence appears in each group. If those numbers are unavailable, mark them unknown. Do not fill the gap with a precise-looking probability. In the example, a different mix of volunteers or a more distinctive trait could change the answer.

Now change the group to 20 helpers and 80 archivists while keeping the same within-group rates. There would be 10 list-loving helpers and 60 list-loving archivists: 60 out of 70, about 86%, would be archivists. The verbal description stayed the same; the population changed.

Read the model with its limits

Slowing down is an opportunity to check an answer, not a guarantee of correctness. A careful calculation can still use bad assumptions. Treat each empirical example as a claim to examine in its own right, including the date and quality of its evidence. Use this book for a broad vocabulary of judgment, and Noise when your question concerns disagreement between reviewers.