Thinking Fast and Slow - Notes

Fast & Slow Thinking                  Daniel Kahneman  (intuitions & biases)


DK in fast & slow – system 1 & 2 thinking says most is the former, fast, intuitive & automatic rather than slow big effort thinking.  K says we pay a price System 1, thinking loves to simplify & jumps wildly to conclusions.


Our brain processes information in 2 distinct ways.


Like when you look at this photo you instantly know she has blond hair, is visibly angry and likely has a few choice words to use.  Without any effort you experienced fast thinking.


If you look at the following problem – something different happens.  17×24 (408)


You knew immediately that this was a multiplication problem, and you probably knew that you could solve it, if you had the energy.  If you do try your muscles will tense, your pupils will dilate and your heart rate will increase.  The process was mental work: deliberate, effortful and orderly – slow thinking.


You had some vague intuitive knowledge of possible results.  You were quick to recognize that both 12,347 and 123 are implausible.  However, without spending time on the problem you could not be certain that the answer was not 568.  Attempt the problem – you experienced slow thinking as you proceeded through a sequence of steps.  You first retrieved from memory the cognitive programme for multiplication that you learned at school and then you implemented it.  Carrying out the computation was a strain.  You felt the burden of holding information in the memory, as you needed to keep track of where you were and where you were going whilst holding on to the intermediate result.  The process was mental work: deliberate, effortful and orderly – slow thinking. 


These 2 systems of fast & slow thinking dictate much of our perception & reaction in life.


Take these 2 lines for example:  Muller-Lyer Illusion.


Its clear that they’re different lengths but if you measure the lines with a ruler they are the same length.  Your S2 now has a new belief you know the lines are equally long.  If asked about their length you can say what you know.  However, S1 fast thinking can’t stop seeing the illusion because it acts automatically.

You have chosen to believe the measurement but you cannot stop S1 from doing its thing.

Lets look at S2 in action.  I’ll show you a string of 4 digits – then add 1 to each number of the original digits. If the card reads 3795 the correct response is 4806.  We’ll go to the next card and you’ll do the same.


3795   add1   4806   add3   6028

6132               7243              9465

7043               8154              10376

9386               10497

1574               2685

2769               3870


Few people can cope with more than 4 digits but even harder with add 3.


Interesting bit is that though your pupils would have dilated (eyeball muscles in stretch) you often become effectively blind when you fully engage S2.

The invisible Gorilla

In a study done by Daniel Simons and Christopher Chabris in 1999, Harvard University over half of the people shown this video did not notice the gorilla – It was as though the gorilla was invisible. This experiment reveals 2 things: that we are missing a lot of what goes on around us, and that we have no idea that we are missing so much. We can be blind to the obvious and blind to our blindness.  Owing to engaged in mental activity When people are focused on something (as they generally are), they often fail to notice surprising situations, other’s perceptions, and problems on their teams.


The study tested the concept of “in-attentional blindness”, where people miss objects in plain sight because they have been told to pay attention to something else. It might seem difficult to believe, but a full 50% of the original study’s participants didn’t notice the gorilla at all.


2010 version: Only 17% of people who were familiar with the original video were able to notice one or both of the unexpected events. On the other hand, 29% of those who hadn’t heard of the first experiment managed to notice one of the other events. Simons explains, “You can make two competing predictions. Knowing about the invisible gorilla might increase your chances of noticing other unexpected events because you know that the task tests whether people spot unexpected events. You might look for other events because you know that the experimenter is up to something. [Alternatively,] knowing about the gorilla might lead viewers to look for gorillas exclusively, and when they find one, they might fail to notice anything else out of the ordinary.”  It definitely appears that the second prediction was the correct one.


A bat & ball costs £1.10p    The bat costs £1 more than the ball. How much does the ball cost?


Chances are your intuition S1 is shouting 10p but the appealing S1 answer is wrong

Do the maths:  if the ball costs 10p and £1.10 for the bat = £1.20p correct answer is 5p

S2 actively checks if the answer is correct.  A failure to check is remarkable because the cost of checking is low: a few seconds of mental effort.  50% of Harvard & Princeton gave the intuitive – incorrect answer.


Even if you worked out the correct answer you likely though of 10p along the way. S1 is trying to work out an answer as quick & seamlessly as possible, which is useful in everyday life.  I.e. walking if every activity reqd full mental effort it would be exhausting.


How many animals of each kind did Moses take on the Ark?   Our brain invests as little resources as necessary so things run quickly & smoothly.  Because Moses is not abnormal in the biblical sense S1 unconsciously detects an association between Moses & Ark and quickly accepts the Q.


System 1 operates automatically and quickly with little or no effort and no sense of voluntary control.

System 2 allocates attention to the effortful mental activities that demand it.  The operations of S2 are often associated with the subjective experience of choice & concentration. 


Both system 1 & 2 are active when you’re awake.  S1 runs automatically and S2 is in low effort mode in which only a fraction of its capacity is engaged.  S1 continuously generates suggestions for S2: impressions, intuitions, intentions and feelings.  If endorsed by S2 impressions and intuitions turn into beliefs and impulse into actions.  Most of the time it runs smoothly.


However, S1 has biases – systematic errors that it’s prone to make.  S1 is gullible and biased to believe.   S2 is in charge of doubting and unbelieving, but sometimes S2 is busy and often lazy. 


Many people are overconfident and prone to place too much faith in their intuitions.


What can be done about biases?  Simple in principle recognize that you are in a cognitive minefield and slow down and ask for reinforcement from S2.  Unfortunately this simple process is unlikely to be followed when it is most needed.  The upshot is that it’s easier to notice a minefield when one of your colleagues is about to walk into it than yourself.


Psychologists refer to two systems in the mind:


When we think of ourselves we identify with S2 the conscious, reasoning self that has beliefs, makes choices and decides what to think about and what to do.


S1 eggs: Complete the phrase bread & …     Detect that one object is more distant than the other;

Orients to the source of a sudden sound; Drive a car on an empty road

Knowledge is stored in memory and accessed without intention or effort.


S2           Focus on the voice of a particular person in a room

Look for a woman with red hair;         Check the validity of a complex argument

Compare 2 TVs for overall value;      Count the occurrences of the letter a in a page of text


S2 operations are effortful – one of its main characteristics is laziness, (laziness is built deep into our nature – the path of least resistance – the law of least effort) a reluctance to invest more energy than is necessary. As a consequence the thoughts & actions that S2 believes that it has chosen are often guided by S1.


S2 is the only one that can follow rules compare objects on several attributes and make deliberate choices bw options.  S1 detects simple relations – they’re all alike.


Busy S2.         Psychological studies have shown that when people are simultaneously challenged by a demanding cognitive task and by a temptation they are more likely to yield to the temptation.  Imagine you are asked to retain a list of 7 digits for a 2 mins.  Whilst your attention is focused on the digits and you’re offered a choice bw 2 desserts: a sinful chocolate cake or a fruit salad. The evidence suggests that you would more likely select the tempting chocolate cake when your mind is loaded with digits.

S1 has more influence on behaviour when S2 is busy – and it has a sweet tooth.


People who are cognitively busy are also more likely to make selfish choices, use sexist language and make superficial judgements in social situations.  A few drinks has the same effects as does a sleepless night.  The self-control of morning people is impaired at night; the reverse is true for night people.

The conclusion is that self-control requires attentions and effort. One of the main functions of S2 is to monitor and control thoughts and actions suggested by S1.


Interesting story.  Reported in Proceedings of the national Academy of Sciences.  Study of 8 parole judges in Israel.  They spend entire days reviewing applications for parole.  The cases are presented in a random order and the spend on average 6 mins per case.  The default decision is denial of parole – only 35% are approved.  The exact time of each decision and morning, lunch & afternoon breaks are recorded. The proportion of approved requests spiked after a break av 65%.  During the 2 hrs until the next feed the rate drops steadily to about zero before the next break.