System 1 Versus System 2

In the 1970’s, social scientists made two assumptions about people. One, people are mostly rational. Two, when they behaved irrationally, it was because emotions such as anger or fear intervened.

Behavioral scientists Daniel Kahneman and Amos Tversky managed to demonstrate that both of these assumptions were false. People did not act rationally most of the time. And when people did act irrationally, it was not because emotions got in the way, but because the design of their cognitive machinery was faulty. Kahneman and Tversky managed to prove this by showing that people made mistakes because of systematic, predictable patterns of thought.

Kahneman summarized these findings in Thinking: Fast and Slow, a book first published in 2011. But the purpose of this work was not to denigrate human intelligence but to show, with more precise language, how our intuitions can deceive us.

He starts by presenting a dichotomy between two systems that represent how the brain functions, System 1 and System 2. Kahneman did not invent these terms (they were previously used in psychology), but he did give them more personality and flavor.

An example of System 1 at work is the narrative fallacy. Consider the description below: Steve is a meek and tidy soul. He has a need for order and structure. He has little interest in people and a passion for detail. Is Steve more likely to be a farmer or a librarian?

Most people will say that Steve is probably a librarian. Why? The story fits. But the problem is that there are so few librarians in any given country, when compared to the number of farmers. So, when asked what is more likely to be Steve’s occupations, System 1 jumps to the conclusion hat Steve’s life fits the narrative given about him, but ignores the fact that there is a base reality which contradicts this narrative (there are so few librarians).

Another example of System 1 at work is the Availability Heuristic. If you have a conversation with your barber, or your cousin, you are more likely going to discuss the most recent thing you learned about, not the most important thing. So, the issues that are most salient in the public mind are rarely important issues, but whatever the media has most recently reported.

At first, Kahneman’s work was criticized, but now it is unanimous: the mind is susceptible to systematic errors because of an overreliance on intuition. That is not to say that intuition is bad. People who are highly experienced would benefit from relying on their intuition, but not all people make intuitive judgments from experience (they often do so with little data or experience).

Definitions of System 1 and System 2

System 1: Fast, involuntary, effortless, immediate (“I like this!”)

“System 1” is a nickname for “automatic system.”

System 1 can think metaphorically, causally, and associatively but not statistically (a mode that requires multiple forms of thinking at once, which are not accessible to system 1.)


  • Complete phrase: “bread and …”
  • Detect hostility in voice. Drive car on empty road.
  • Recognize “meek and tidy soul with a passion for detail” resembles an occupational stereotype.

System 2: Slow, voluntary, effortful, deliberate (should I like this?).

“System 2 is a nickname for effortful system.”

Operations of system 2 are associated with subjective experience of agency, choice, and concentration.


  • Fill out a tax form.
  • Tell someone your phone number.
  • Check the validity of a complex logical argument.

After learning that your mind is subject to many cognitive illusions, the obvious question is: can these cognitive illusions be overcome?

Probably not.

System 2 would need to put in too much effort to make sure that no System 1 errors are made — a tedious, impractical way to live life. But, a compromise is possible. Recognize situations where system 1 errors are likely and the stakes are high.

“In the unlikely event of this book being made into a film, System 2 would be a supporting character who believes herself to be the hero.”

The funny thing is that System 2 thinks it is in charge, but it is not. System 2 is more like the secretary or the assistant. System 1 generated complex ideas, but only System 2 can order them. This gives System 2 a very important role, but it is not in command most of the time.

System 2 deals with purposeful questions, whether from abroad or from within. There is no limit to what these questions can be, but they must be specific. System 1 constantly monitors what is happening internally and externally. These basic assessments play an important role in intuitive judgement because they substitute for more difficult — that is the idea behind heuristics and biases.

System 1 has been shaped by evolution to provide a continuous assessment of main survival problems. Is everything normal? Is there a threat or a major opportunity? Should I approach or avoid? How are things going? Even though less relevant today in ancestral past, our brains still work this way.

System 1 substitutes complex questions for simpler ones: You rarely feel stumped. Even if you don’t really understand something, you make conclusions based on a small amount of evidence that you don’t understand. You like some people and dislike others. You feel a stock will succeed. You distrust a stranger. All of this is seamless to you. The experience of life feels a lot more straightforward than it really is.

“This is your system 1 talking. Slow down to let your system 2 take control”

End of Thinking Fast and Slow

These researchers have mapped our activities into (roughly) a dual mode
of thinking, which they separate as “System 1” and “System 2 , “ or the experiential and the cogitative. The distinction is straightforward.
System 1, the experiential one, is effortless, automatic, fast, opaque (we
do not know that we are using it), parallel-processed, and can lend itself
to errors. It is what we call “intuition,” and performs these quick acts of
prowess that became popular under the name blink, after the title of Malcolm Gladwell’s bestselling book. System 1 is highly emotional, precisely
because it is quick. It produces shortcuts, called “heuristics,” that allow us
to function rapidly and effectively. Dan Goldstein calls these heuristics
“fast and frugal.” Others prefer to call them “quick and dirty.” Now,
these shortcuts are certainly virtuous, since they are rapid, but, at times,
they can lead us into some severe mistakes. This main idea generated an
entire school of research called the heuristics and biases approach (heuristics corresponds to the study of shortcuts, biases stand for mistakes).
System 2, the cogitative one, is what we normally call thinking. It is what
you use in a classroom, as it is effortful (even for Frenchmen), reasoned,

slow, logical, serial, progressive, and self-aware (you can follow the steps
in your reasoning). It makes fewer mistakes than the experiential system,
and, since you know how you derived your result, you can retrace your
steps and correct them in an adaptive manner.
Most of our mistakes in reasoning come from using System 1 when we
are in fact thinking that we are using System 2. How? Since we react without thinking and introspection, the main property of System 1 is our lack
of awareness of using it!
Recall the round-trip error, our tendency to confuse “no evidence of
Black Swans” with “evidence of no Black Swans”; it shows System 1 at
work. You have to make an effort (System 2) to override your first reaction. Clearly Mother Nature makes you usé the fast System 1 to get out of
trouble, so that you do not sit down and cogitate whether there is truly a
tiger attacking you or if it is an optical illusion. You run immediately, before you become “conscious” of the presence of the tiger.
Emotions are assumed to be the weapon System 1 uses to direct us and
force us to act quickly. It mediates risk avoidance far more effectively than
our cognitive system. Indeed, neurobiologists who have studied the emotional system show how it often reacts to the presence of danger long before we are consciously aware of it-we experience fear and start reacting
a few milliseconds before we realize that we are facing a snake.
Much of the trouble with human nature resides in our inability to use
much of System 2, or to use it in a prolonged way without having to take
a long beach vacation. In addition, we often just forget to use it.

Beware the Brain
Note that neurobiologists make, roughly, a similar distinction to that between System 1 and System 2, except that they operate along anatomical
lines. Their distinction differentiates between parts of the brain, the cortical part, which we are supposed to use for thinking, and which distinguishes us from other animals, and the fast-reacting limbic brain, which is
the center of emotions, and which we share with other mammals.

As a skeptical empiricist, I do not want to be the turkey, so I do not
want to focus solely on specific organs in the brain, since we do not observe brain functions very well. Some people try to identify what are called
the neural correlates of, say, decision making, or more aggressively the
neural “substrates” of, say, memory. The brain might be more complicated machinery than we think; its anatomy has fooled us repeatedly in

the past. We can, however, assess regularities by running precise and thorough experiments on how people react under certain conditions, and keep
a tally of what we see.
For an example that justifies skepticism about unconditional reliance
on neurobiology, and vindicates the ideas of the empirical school of medicine to which Sextus belonged, let’s consider the intelligence of birds. I
kept reading in various texts that the cortex is where animals do their
“thinking,” and that the creatures with the largest cortex have the highest
intelligence-we humans have the largest cortex, followed by bank executives, dolphins, and our cousins the apes. Well, it turns out that some
birds, such as parrots, have a high level of intelligence, equivalent to that
of dolphins, but that the intelligence of birds correlates with the size of another part of the brain, called the hyperstriatum. So neurobiology with its
attribute of “hard science” can sometimes (though not always) fool you
into a Platonified, reductive statement. I am amazed that the “empirics,”
skeptical about links between anatomy and function, had such insight-
no wonder their school played a very small part in intellectual history. As
a skeptical empiricist I prefer the experiments of empirical psychology to
the theories-based MRI scans of neurobiologists, even if the former appear
less “scientific” to the public.

Originally published at

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