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2.2  Categories and common nouns
Appendices

2.2 

Categories and common nouns

The limitations of proper nouns

What would the disadvantages be of a language that contained only names, that is, words that applied to individual things (or situations)?

Names (in the form of proper nouns) buy our Prelings a lot. They can now call the attention of the members of their tribe to some of the important objects in their environment. But they can only do this for the objects that have names assigned to them. For each individual object, being named requires the following:

  1. The members of the tribe can all identify the object.
  2. The members of the tribe agree on the name for the object, that is, the form of the word.
  3. Each member remembers the name so that the form can be recalled when the Preling wants to refer to the individual and the name can be understood when another member of the tribe uses it.

Imagine the following situation. You have been out foraging around and have discovered a previously unknown person, apparently a member of another tribe, hiding near a large rock on the opposite side of the nearby river. Your tribe has an agreed-on name for the river but, though everyone is certainly familiar with the rock, no one has felt the need to refer to it before so it has no name. And because the new person is unknown to everyone in the tribe but you, that person can't have a name. You would desperately like to refer to these two individuals, the rock and the new person, but you can't. You need something more than simple names.

But names have another inadequacy. Recall one of the themes of this book, that language is constrained by the bodies and the cognitive capacities of language users. Now consider what it would be like to have a name, a separate proper noun, like Lois or Detroit, for every individual object you might ever refer to. Even if the members of your tribe could agree on the names, the limits of long-term memory would get in the way: how would you ever remember the millions of different names that you'd need?

It was convenient to begin the discussion of words and meaning with names, but for the reasons given above, maybe we shouldn't consider them to be the most basic kind of words.

Categories

The solution to the problems associated with names is provided by another basic human (and Preling) capacity, the capacity to categorize. People group objects in the world into categories on the basis of their similarities. Not only can we find individual apples, cats, and mountains in the world and distinguish individual apples, cats, and mountains from one another; we can categorize objects as being apples (and not pears or grapes), cats (and not dogs or goats), or mountains (and not valleys or boulders). An apple is an apple, that is, an instance of the category apple, because it shares properties with other apples. Apples tend to have a characteristic shape, a characteristic taste and smell (though there are of course a number of variations), and a characteristic size (though there is again a range of precise possibilities), and they grow on a type of tree with typical properties of its own.

Categories are in the mind, not in the world.

Our categories are to some extent natural; they correspond to relatively clean divisions in the world. Thus it's not just that we think apples are different from pears; they actually are. However, rather than thinking of categories as features of the world, we will be viewing them as cognitive entities, as concepts. This is because people clearly have the capacity to come up with categories for things that exist only in their imagination and because different cultures, and different people with the same culture, may categorize the same set of individuals differently. We'll see throughout this book how the similarities and differences between languages can give us insight into how human categorization works.

What good are categories? They permit people to respond in a similar fashion to many different objects once the objects can be categorized. Thus once you know an object is an instance of the category apple, you know that you can eat it or cut it up and put it in a pie. You don't have to learn separately for each individual apple what sorts of behaviors are possible.

Using and learning categories

Before we go on and relate categories to language, we need to remind ourselves that we should be considering process as well as product. Rather than think of categories as things in the mind, it will usually be more useful to think in terms of the process of categorization,wikipedia how a person figures out what category something belongs to so that they can then behave in an appropriate way for that thing (eat it, approach it, run from it, etc.). As with individuals, we can think of categories as a localized or distributed in the mind of the categorizer. For now, we'll assume that they are localized, that is, that there is a place in long-term memory dedicated to each category that the Preling or person knows. In such a system, categorization of an object of some sort would normally start with some perceptual input, that is, something seen, heard, felt, smelled, and/or tasted by the categorizer. This would then activate the places in memory dedicated to particular perceptual features. that are associated with the object being perceived. If these features overlap enough with the features in a category C and don't overlap more with the features of some other category, then the place in memory for category C is activated. The figure below illustrates this process. Some of the features (small squares) are activated by the perceptual input (activated features appear in green), and these are associated with two categories, apple and pear, but more strongly with apple, so it is activated.

The processing perspective also reminds us that categories like apple are not innate; they have to be learned. So a complete theory of categorization would also have to explain the learning process. But going into that now would lead us too far afield.

Common nouns

Now let's assume our Prelings have this powerful categorizing capacity. (There is good reason to believe that we're not the only animals that have it, by the way.) All we need to extend their primitive communcation system in a powerful way is to associate words with some of the categories. Human languages have such words; we will call them common nouns, words like apple, cat, and mountain. Now when a Preling wants to refer to an individual and doesn't have a name for it, there is still an out. If the Preling can categorize the individual and can find a common noun for that category in long-term memory, then they can use that noun to refer to the object. Of course the Hearer now has a new problem, that of figuring out which instance of the category the Speaker is talking about. If the Speaker says "rock", which rock is intended? For both Speaker and Hearer, there is clearly a lot of linguistic work to be done in using common nouns. But think how much more versatile the Prelings' communication system has become. With names they could only refer to the small set of individuals that had words assigned to them. Now they have the potential to refer to an infinite number of individuals, that is, all of the instances of all of the categories they have names for.

Probably because they are so frequent in our speech and because their function is not so complex, common nouns are among the first words that babies learn, at least in many languages. Babies' utterances early in their second year usually consist of single words, and many of these are common nouns such as juice or kitty. As with proper nouns, we have to be careful in interpreting children's utterances; when these words first appear, it is not necessarily the case that children are using them to refer to objects. They may simply have learned to respond with a particular word form when they are in the presence of particular things.

What categories are

When we want to find the meaning of a word, we often look it up in a dictionary. But remember that linguists are interested in describing the knowledge and behavior that ordinary native speakers of a language have. For linguists, why would dictionary definitions not work very well as accounts of word meaning?

The inadequacy of dictionary definitions

What's the best way to describe human categories, including those that common nouns are associated with? Or alternately, what form do categories take in the mind? Or alternately, how do nouns mean? This question is one of the hardest and most contentious in the study of language, and there is no agreed-on answer. One possibility would be something like the definition in a dictionary. Here is Webster's definition for apple: "the fleshy usually rounded and red or yellow edible pome fruit of a tree (genus Malus) of the rose family". This seems to be on the right track, but it includes words like pome, which most native speakers (including me) don't know and the relationship between apples and roses, which, if people know it, doesn't seem central to their knowledge of apples. (In any case, a three-year-old, who may have no difficulty understanding and using the word apple, wouldn't normally know about this relationship.) Also the definition conveys nothing of what it feels like to bite into an apple, which for many people probably has something to do with what the word suggests to them.

Another problem with dictionary definitions as a model of what we know about words is that they are in the language that they are defining. It is hard to imagine how a child who still knows almost nothing about the grammar of the language would be learning meanings in the form of complex expressions in the language that is being learned. Some linguists and philosophers of language have tried to come up with meanings for words that are somewhat like dictionary definitions, expressed in a kind of "language of thought,"wikipedia which all children supposedly already somehow know. But there have been problems with this view since it has been difficult to come up with definitions that hold in all cases. There always seem to be exceptions. Even for something as concrete and seemingly obvious as an apple, nothing seems to be absolutely necessary. Does it have to have a peel and a core? No, a peeled or a cored apple is still an apple. A particular texture? It would strike us as strange, but something that is like an apple in every other way, but has the texture of butter, say, would still be an apple.

Another way of looking at the problem of exceptions is to ask what the necessary and sufficient conditionswikipedia are for membership in a category. Necessary conditions are those that must be true for all members of the category. Thinking in terms of necessary conditions means taking the perspective of the Hearer. When a Hearer hears a noun like apple or horse, they would like to be able to know what properties the referent has. If the word is horse, can they infer without question that the thing referred to has four legs? Well, no, a three-legged horse is still a horse. It seems that, except in scientific contexts, when nouns need to be used in very precise ways, natural human categories cannot be defined in terms of necessary conditions.

Sufficient conditions are the set of properties that must be true of a thing before we can conclude that it is a member of a category. Thinking in terms of sufficient conditions means taking the perspective of the Speaker. Given an object to be referred to, a Speaker has to categorize it on the basis of the properties it has and then find a word that's associated with the category. It seems just as difficult to come up with a set of sufficient conditions for a category as with a set of necessary conditions. To categorize something as a horse, is it enough to know that it has typical horse features on its head and body? What if it has those features but only because what we're seeing is a horse costume worn by two people? And what exactly are the typical head and body features anyway?

"Good" and "bad" apples

One popular idea among linguists and psychologists is that a category takes the form of a prototype,wikipedia a typical member of the category. For example, for me a prototypical apple is something like a Red Delicious: red, about 6 cm across, and relatively sweet. The prototype may include sensory features (e.g., what it looks and tastes like) and features that have to do with function (what you do with it). On this view, category membership is not an all-or-none matter; an individual is a more or less good member of a category depending on how close it is to the prototype. A Granny Smith is an apple but not as "good" an apple as a Red Delicious for me. And a crabapple is even "worse."

The prototype idea makes sense because objects take more or less time for people to label with nouns or to identify when they hear the nouns. This has been shown, for example, for birds. Americans are faster to call a robin a bird than to call a chicken, an ostrich, or a penguin a bird. I would probably come up with the noun apple faster when I'm labeling a Red Delicious than when I'm labeling a Granny Smith. And I would think of or find a Red Delicious faster than a Granny Smith when I hear the word apple. Note how the prototype idea also avoids the problem of necessary and sufficient conditions. A three-legged horse may not match the horse prototype perfectly, but it can still be considered a horse, just an atypical one, that is, not a very "good" horse.

There are still other proposals for what categories are. A quite radical one, but one that has been shown to agree with lots of data on categorization, is the exemplar-based theory (actually a whole family of related theories). In this approach there is no explicit representation of categories at all. Each category is just the set of all of the instances of that category that have been remembered (many imperfectly). What is an apple on this view? It is all of the individual apples that remain in the mind of a particular person. And hearing the word apple results in some combination of all of these being recalled all at once.

We will be meeting categories of one type or another in every section of this book. In fact to a large extent, the study of language is the study of linguistic categories. As we discuss these categories in more detail, it will sometimes be possible to ignore the details of how categories are represented and how categorization works, but at other times we'll have to consider how a prototype theory or an exemplar-based theory would differ.

Masses, things, and a lexicon

Before we go on, let's extend the range of things our Prelings can refer to. Say a Preling has noticed some smoke coming from across the river, a possible sign of another tribe, and wants to report this to the others. Smoke is not an object since it doesn't have well-defined boundaries, although, like objects, it does have characteristic and relatively constant properties, its color, its smell, the way it moves in the wind. We will refer to such things as masses. In human languages, masses tend to be referred to by words that are similar to the words used for referring to objects. Some English examples are fog, water, clay, wood, and soup. Like speakers of English and most other modern languages, our Prelings will use common nouns for masses as they do for objects. We will refer to the meta-category of objects and masses as things. Things are characterized by a set of relatively stable properties.

Our Prelings now have the potential for a very large set of words, as many as the categories that they group the things in their world into. Modern humans may know tens of thousands of nouns for the categories they need to refer to. While the Prelings are at this stage very far from having full-blown human language, they do have the beginnings, so it is time to change their name. They now have a lexicon, a mental dictionary of words, so we will call them Lexies.


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