Daniel Kahneman’s theory Kahneman begins by explaining the purpose of his book: to provide people with a richer vocabulary for discussing and identifying errors in judgment. He briefly traces his professional interest in the psychology of judgment and decision-making, illustrated with examples of human intuition's successes and failures. Lastly, Kahneman offers a broad overview of Thinking, Fast and Slow, starting with the functions of two complementary "systems" of cognition and describing the heuristics, or rules of thumb, these systems depend on. In the "Origins" section of the introduction, Kahneman discusses his research and his late thought partner, Amos Tversky, at length. Tversky's contributions were central to Kahneman's work and success.