Excerpt from Thinking, Fast and Slow by Daniel Kahneman, plus links to reviews, author biography & more

In rough order of complexity, here are some examples of the automatic activities that are attributed to System 1:

• Detect that one object is more distant than another.
• Orient to the source of a sudden sound.
• Complete the phrase "bread and..."
• Make a "disgust face" when shown a horrible picture.
• Detect hostility in a voice.
• Answer to 2 + 2 = ?
• Read words on large billboards.
• Drive a car on an empty road.
• Find a strong move in chess (if you are a chess master).
• Understand simple sentences.
• Recognize that a "meek and tidy soul with a passion for detail" resembles an occupational stereotype.

All these mental events belong with the angry woman - they occur automatically and require little or no effort. The capabilities of System 1 include innate skills that we share with other animals. We are born prepared to perceive the world around us, recognize objects, orient attention, avoid losses, and fear spiders. Other mental activities become fast and automatic through prolonged practice. System 1 has learned associations between ideas (the capital of France?); it has also learned skills such as reading and understanding nuances of social situations. Some skills, such as finding strong chess moves, are acquired only by specialized experts. Others are widely shared. Detecting the similarity of a personality sketch to an occupational stereotype requires broad knowledge of the language and the culture, which most of us possess. The knowledge is stored in memory and accessed without intention and without effort.

Several of the mental actions in the list are completely involuntary. You cannot refrain from understanding simple sentences in your own language or from orienting to a loud unexpected sound, nor can you prevent yourself from knowing that 2 + 2 = 4 or from thinking of Paris when the capital of France is mentioned. Other activities, such as chewing, are susceptible to voluntary control but normally run on automatic pilot. The control of attention is shared by the two systems. Orienting to a loud sound is normally an involuntary operation of System 1, which immediately mobilizes the voluntary attention of System 2. You may be able to resist turning toward the source of a loud and offensive comment at a crowded party, but even if your head does not move, your attention is initially directed to it, at least for a while. However, attention can be moved away from an unwanted focus, primarily by focusing intently on another target.

The highly diverse operations of System 2 have one feature in common: they require attention and are disrupted when attention is drawn away. Here are some examples:

• Brace for the starter gun in a race.
• Focus attention on the clowns in the circus.
• Focus on the voice of a particular person in a crowded and noisy room.
• Look for a woman with white hair.
• Search memory to identify a surprising sound.
• Maintain a faster walking speed than is natural for you.
• Monitor the appropriateness of your behavior in a social situation.
• Count the occurrences of the letter a in a page of text.
• Tell someone your phone number.
• Park in a narrow space (for most people except garage attendants).
• Compare two washing machines for overall value.
• Fill out a tax form.
• Check the validity of a complex logical argument.

In all these situations you must pay attention, and you will perform less well, or not at all, if you are not ready or if your attention is directed inappropriately. System 2 has some ability to change the way System 1 works, by programming the normally automatic functions of attention and memory. When waiting for a relative at a busy train station, for example, you can set yourself at will to look for a white-haired woman or a bearded man, and thereby increase the likelihood of detecting your relative from a distance. You can set your memory to search for capital cities that start with N or for French existentialist novels. And when you rent a car at London's Heathrow Airport, the attendant will probably remind you that "we drive on the left side of the road over here." In all these cases, you are asked to do something that does not come naturally, and you will find that the consistent maintenance of a set requires continuous exertion of at least some effort.

Thinking, Fast and Slow Copyright © 2011 by Daniel Kahneman