Thinking, Fast and Slow

Kahneman opens by allowing us to observe our minds in two different processing modes. He first provides an image of an angry-looking woman, eyebrows furrowed and mouth agape. He tells readers to note how they automatically observe her to be angry, perhaps about to say something loud and unkind. He says that this is an instance of “fast thinking.”

Next, Kahneman instructs us to solve the problem 17 x 24. He states that we know we could probably solve the problem with effort, and perhaps with paper and pencil. He notes that when we solve it, we proceed through a sequence of steps, burdened by holding information in our heads. This is an example of slow thinking.

Kahneman adopts the terms used by psychologists Keith Stanovich and Richard West, who referred to these two processes as “System 1” and “System 2.”  System 1 operates automatically and quickly. System 2 allocates attention to complex and effortful mental activities.

Kahneman then lists some examples of System 1 and System 2 processing: System 1 detects distance, orients to sounds, allows us to drive a car on an empty road, automatically answers 2 + 2 = ?, reads words, and understands simple sentences. System 1, Kahneman says, is responsible for “effortlessly originating impressions and feelings.” Kahneman also notes that many of these mental actions are completely involuntary.

System 2, on the other hand, is responsible for thoughts and actions that require attention, and which are disrupted if attention is drawn away. This includes focusing on a single voice in a crowded room, looking for a woman with white hair, counting the instances of the letter “a” on a page, comparing two washing machines for value, and checking the validity of a complex logical argument. These things do not come naturally and require exertion of at least some effort.

Kahneman writes that the phrase “pay attention” is apt, because we have a limited budget of attention to allocate. We cannot calculate 17 x 24 when driving a car in heavy traffic—we must focus on one activity or the other.

Kahneman illustrates this concept in a famous study conducted by Christopher Chabris and Daniel Simons. They showed participants a short film of two teams—one wearing white and one wearing black—passing basketballs. The viewers are instructed to count the passes of the white team and ignore the team with black shirts. Most people become so focused on the task, and about half of them do not notice a woman wearing a gorilla suit who appears, crosses the court, thumps her chest, and moves on. The gorilla study shows that we can be blind to the obvious, and blind to our blindness.

When System 1 runs into difficulty, it calls on System 2 to support it, as in the problem of 17 x 24. System 2 also comes into play when people experience a surprise that violates the expected model of the world (such as when they notice a person in a gorilla suit in a basketball game), because it then tries to make sense of the surprising stimulus. System 2 also continuously monitors a person’s behavior and works to maintain self-control.

The division of labor between System 1 and System 2 is highly efficient, minimizing effort. System 1 is generally sufficient and its models of familiar situations are generally accurate. It does have biases, however, and it cannot be turned off.

Kahneman then asks readers to participate in an experiment, reading two sets of words. In each set, there are two columns (a left and right column). Some of the words are in all upper-case letters, and some of them are in all lower-case letters. The difference between the two sets is that in the left set, the words alternate between “left” and “right.” In the right set, the words alternate between “upper” and “lower.” Kahneman asks people to complete two tasks: first calling out whether the words a person is reading is in upper or lower case, and then calling out whether the word is printed to the left of center or the right of center.

What Kahneman reveals, and what we find when we participate, is that it is easier to call out whether the word is in upper or lower case if we are not reading the words “upper” and “lower,” and that it is easier to call out whether the word is printed to the left or right if we are not reading the words “left” and “right.” It is harder to carry out the task when there is a conflict between that task and an automatic response (reading the word itself). System 2 is called in to overcome the impulses of System 1.

Kahneman next introduces illusions, including a famous image called the Müller-Lyer illusion. It shows two figures: on the top is a horizontal line with arrows or fins attached to it, that point outward, away from the line. On the bottom is another horizontal line with arrows or fins that point inward, towards the line. Even though measuring would reveal that the two horizontal lines are the same, the horizontal line in the bottom figure always appears longer. Thus, even though we believe that the two lines are equally long, that is not our impression of it.

The Müller-Lyer illusion is an example of a visual illusion, but there are cognitive illusions as well. As a graduate student, Kahneman attended courses on psychotherapy. One professor said that the students might meet a patient who will share a tale of mistakes in his past treatment, but who feels that they (the students) will be able to help—a feeling the students would share. The professor then tells them that despite their sympathy and their intuition, they would not be able to help this patient, as he is likely a psychopath.

Kahneman understands that it is impractical to constantly question our own thinking. But he writes that what we can do is learn to “recognize situations in which mistakes are likely and try harder to avoid significant mistakes when the stakes are high.”

Kahneman then includes a disclaimer by saying that he talks about System 1 and System 2 as though they have personalities, abilities, limitations, and agency. He says that this way of speaking is considered taboo in his professional circles because they conjure up images of little people inside a person’s head. But Kahneman explains that he only uses the two terms as a shorthand, and using the two systems as the subjects of sentences makes it easier for people to understand those sentences.