It is obvious that language is a crucial tool for
communication. Every animal communicates
in some way. Right now, my dog is
barking at the window to warn a deer outside to get off the lawn. Male songbirds announce their availability by
whistling in the trees. Even ants use
chemical signals that allow other ants to follow paths they have taken.
We have language, though, and that supports a tremendous
range of communication abilities. It
even allows me to communicate with you across time and space. I am typing this now sitting at a table in my
house. Some time in the future, you will
read these words while sitting at a computer or iPad or smart phone.
This incredible tool that enables us to communicate also
supports all kinds of sophisticated thinking abilities. One in particular that is quite amazing is
our ability to use words to name things.
Some of our words are proper names that label specific individuals. Standing in a crowd, if someone yells out,
“Art,” I will turn around, but most everyone else will keep on walking. That label refers to me.
Other labels refer to categories that are described by the
properties that they have. A dog (like
mine who is now lying on the sofa watching me type) names a small animal that
usually has four legs and teeth and is often kept at home as a pet. When we use this label, we are referring to
things that generally have this collection of properties. These property-based categories are very
common.
One of the most fascinating kinds of categories is what Hunt
Stilwell and I called role-governed
categories in a 2001 paper that we published in the Journal of Experimental and Theoretical Artificial Intelligence. These categories provide a name for things
that play a particular role in a situation.
For example, a pet is (usually)
an animal that people keep and take care of as a companion at home. It doesn’t really matter what kind of an
animal it is as long as it plays this role.
People can have dogs, cats, birds, fish, lizards, and pigs as pets. If these animals are not being kept as a
companion then they are not pets, so the role they are playing is crucial for
being able to use this label.
There is growing evidence that these role governed
categories differ from other kinds of categories. For example, Micah Goldwater, Hunt Stilwell
and I have a paper coming out soon in Cognition
that explores the kinds of things that people think are true of different kinds
of categories. When you ask people to
list the things that are typically true of property-based categories like dog, they tend to list features of the
object like furry, barks, or cute. When
you ask them to list things that are typically true of role-governed
categories, though, they tend to list properties that relate that the object to
other things. Listing properties of a pet, people say things like “lives with
an owner,” or “provides companionship.”
In addition, when people think about typical members of a
category, they do that differently for role-governed categories than for other
kinds of categories. When people think
of a typical property-based category, they tend to think of an average or
prototype. The typical dog is medium-sized,
furry, and friendly. Labs and Golden
Retrievers are typical dogs. Chihuahuas
and Great Danes are less typical dogs.
When people think of typical role-governed categories,
though, they tend to think about ideal members of the category. For example, a typical pet is easy to take
care of, affectionate, and loyal. That
is close to what people’s ideal pet is.
Having words that refer to roles is something that helps
make people smart. These labels help us
to recognize when we see some new object that also plays the same role in a
situation. That allows us to extend
these roles to new cases. When I was in elementary school, there was a
fad to create pet rocks. A pet rock was
different from a regular rock, because people took care of them and often
painted them and treated them specially.
A friend of mine in grad school had a boyfriend that she used to take
care of and feed, and we referred to him as her pet. When someone at work has a task they work on
and nurture over time, we refer to it as a pet project.
Without these words, it would be difficult for us to notice
that the same role has come up again. As
beautiful as the song of a songbird is, it will never be able to recognize what
a pet is, because it does not have
the thinking abilities that support the kind of sophisticated language that
people have.
