Daniel Kahneman Nobel Lecture

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rent stimulation. Intuitive judgments deal with concepts as well as with per-

cepts, and can be evoked by language.

In the model that will be presented here, the perceptual system and the in-

tuitive operations of System 1 generate impressions of the attributes of objects

of perception and thought. These impressions are not voluntary and need

not be verbally explicit. In contrast, judgments are always explicit and inten-

tional, whether or not they are overtly expressed. Thus, System 2 is involved

in all judgments, whether they originate in impressions or in deliberate rea-

soning. The label ‘intuitive’ is applied to judgments that directly reflect im-

pressions. As in several other dual-process models, one of the functions of

System 2 is to monitor the quality of both mental operations and overt be-

havior (Gilbert, 2002; Stanovich & West, 2002). In the anthropomorphic

terms that will be used here, the explicit judgments that people make

(whether overt or not) are endorsed, at least passively, by System 2.

Kahneman and Frederick (2002) suggested that the monitoring is normally

quite lax, and allows many intuitive judgments to be expressed, including

some that are erroneous.

Shane Frederick (personal communication, April 2003) has used simple

puzzles to study cognitive self-monitoring, as in the following example: “A bat

and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much

does the ball cost?” Almost everyone reports an initial tendency to answer “10

cents” because the sum $1.10 separates naturally into $1 and 10 cents, and 10

cents is about the right magnitude. Frederick found that many intelligent

people yield to this immediate impulse: 50% (47/93) of Princeton students,

and 56% (164/293) of students at the University of Michigan gave the wrong

answer. Clearly, these respondents offered a response without checking it.

The surprisingly high rate of errors in this easy problem illustrates how light-

ly the output of System 1 is monitored by System 2: people are not accus-

PERCEPTION

REASONING

SYSTEM 2

INTUITION

SYSTEM 1

Fast

Parallel

Automatic

Effortless

Associative

Slow-learning

Slow

Serial

Controlled

Effortful

Rule-governed

Flexible

Percepts

Current stimulation

Stimulus-bound

Conceptual representations

Past, Present and Future

Can be evoked by language

PROCESS

CONTENT

Figure 1.

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452

tomed to thinking hard, and are often content to trust a plausible judgment

that quickly comes to mind. Remarkably, errors in this puzzle and in others of

the same type were significant predictors of relative indifference to delayed

rewards (high discount rates), and of cheating.

The accessibility dimension

The core concept of the present analysis of intuitive judgments and prefer-

ences is accessibility – the ease with which particular mental contents come to

mind (Higgins, 1996). A defining property of intuitive thoughts is that they

come to mind spontaneously, like percepts. To understand intuition, then, we

must understand why some thoughts are accessible and others are not. The

concept of accessibility is applied more broadly in this treatment than in com-

mon usage. Category labels, descriptive dimensions (attributes, traits), values

of dimensions, all can be described as more or less accessible, for a given in-

dividual exposed to a given situation at a particular moment. 

For an illustration of differential accessibility, consider Figures 2a and 2b.

As we look at the object in Figure 2a, we have immediate impressions of the

height of the tower, the area of the top block, and perhaps the volume of the

tower. Translating these impressions into units of height or volume requires a

deliberate operation, but the impressions themselves are highly accessible.

For other attributes, no perceptual impression exists. For example, the total

area that the blocks would cover if the tower were dismantled is not percep-

tually accessible, though it can be estimated by a deliberate procedure, such

as multiplying the area of a block by the number of blocks. Of course, the sit-

uation is reversed with Figure 2b. Now the blocks are laid out and an impres-

sion of total area is immediately accessible, but the height of the tower that

could be constructed with these blocks is not.

Some relational properties are accessible. Thus, it is obvious at a glance

Figure 2a.

Figure 2b.

Figure 2c.

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that Figures 2a and 2c are different, but also that they are more similar to

each other than either is to Figure 2b. And some statistical properties of en-

sembles are accessible, while others are not. For an example, consider the

question “What is the average length of the lines in Figure 3?” This question

is easy. When a set of objects of the same general kind is presented to an ob-

server – whether simultaneously or successively – a representation of the set is

computed automatically, which includes quite precise information about the

average (Ariely, 2001; Chong & Treisman, in press). The representation of

the prototype is highly accessible, and it has the character of a percept: we

form an impression of the typical line without choosing to do so. The only

role for System 2 in this task is to map this impression of typical length onto

the appropriate scale. In contrast, the answer to the question “What is the to-

tal length of the lines in the display?” does not come to mind without consid-

erable effort.

These perceptual examples serve to establish a dimension of accessibility.

At one end of this dimension we find operations that have the characteristics

of perception and of the intuitive System 1: they are rapid, automatic, and ef-

fortless. At the other end are slow, serial and effortful operations that people

need a special reason to undertake. Accessibility is a continuum, not a di-

chotomy, and some effortful operations demand more effort than others.

The acquisition of skill selectively increases the accessibility of useful re-

sponses and of productive ways to organize information. The master chess

player does not see the same board as the novice, and the skill of visualizing

the tower that could be built from an array of blocks could surely be im-

proved by prolonged practice. 

Determinants of accessibility

As it is used here, the concept of accessibility subsumes the notions of stimu-

lus salience, selective attention, and response activation or priming. The dif-

ferent aspects and elements of a situation, the different objects in a scene,

and the different attributes of an object – all can be more or less accessible.

What becomes accessible in any particular situation is mainly determined,

Figure 3.

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