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.