240 • CHAPTER 9 Knowledge

Why is it difficult to

decide if a particular

object belongs to a

particular category, such

as “chair,” by looking up its

definition? (241)

How are the properties

of various objects “filed

away” in the mind?

(243, 256)

How is information

about different categories

stored in the brain? (260)

Can young infants

respond to the categories

“cat” and “dog”? (263)

Some Questions We Will Consider

I

magine that you find yourself in an unfamiliar town, where you have never

been before. As you walk down the street, you notice that many things are not exactly

the same as what you would encounter if you were in your own town. On the other

hand, there are lots of things that seem familiar. Cars pass by, there are buildings on

either side of the street and a gas station on the corner, and a cat dashes across the

street and makes it safely to the other side. Luckily, you know a lot about cars, build-

ings, gas stations, and cats, so you have no trouble understanding what is going on.

You know about the various components of this street scene because your mind is

full of concepts. A concept is a mental representation that is used for a variety of cog-

nitive functions, including memory, reasoning, and using and understanding language

(Solomon et al., 1999). Thus, when you think about cats, you are drawing on your

concept, or mental representation, of cats, which includes information about what cats

are, what they usually look like, how they behave, and so on.

By far the most commonly studied function of concepts is categorization, which is

the process by which things are placed into groups called categories. For example, when

you see vehicles in the street you can place them into categories such as cars, SUVs,

Chevrolets, Fords, American cars, and foreign cars. Categories are not simply conve-

nient ways of sorting objects. They are tools that are essential for our understanding

of the world.

One of the most important functions of categories is to help us to understand individ-

ual cases we have never seen before. For example, being able to say that the furry animal

across the street is a “cat” provides a great deal of information about it (● Figure 9.1).

Categories have therefore been called “pointers to knowledge” (Yamauchi & Markman,

2000). Once you know that something is in a category, whether “cat,” “gas station,” or

“impressionist painting,” you know a lot of general things about it and can focus your

energy on specifying what’s special about this particular object (see Solomon et al., 1999;

Spalding & Murphy, 1996).

Being able to place things in categories can also help us understand behaviors

that we might otherwise fi nd baffl ing. For example, if we see a man with the left

side of his face painted black and the right side painted gold, we might wonder

what is going on. However, once we note that the person is heading toward the

football stadium and it is Sunday afternoon, we can categorize the person as a

“Pittsburgh Steelers fan.” Placing him in that category explains his painted face

and perhaps other strange behaviors that happen to be normal on game day in

Pittsburgh (Solomon et al., 1999).

These various uses of categories testify to their importance in everyday life. It is

no exaggeration to say that if there were no such thing as categories, we would have a

very diffi cult time dealing with the world. Consider what it would mean if every time

you saw a different object, you knew nothing about it other than what you could fi nd

out by investigating it individually. Clearly, life would become extremely complicated

if we weren’t able to rely on the knowledge provided to us by categories. Given the

importance of categories, cognitive psychologists have been interested in determining

the process involved in categorizing objects.

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