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2.3  Word senses and taxonomies


Word senses and taxonomies

Word senses

As cultures develop, they create or learn about new categories of things, for example, tools, and they then have the need to refer to these new things. Where might the words for the new categories come from?

We have seen that words — common nouns — are associated with categories of things. I will refer to those categories that make up the meanings of words as semantic categories. As already noted, people also have plenty of categories that have no words associated with them. In fact which categories have labels varies from person to person and from language to language, as we will see soon. One way to summarize what we've discussed so far is shown in the figure below. So far the situation I've described looks like the following:

In the figure the word form is connected to the word's meaning, a semantic category, by an arrow that I will use to indicate a meaning relation. The arrow has two heads because a Speaker can get from a semantic category to a word form, and a Hearer can get from a word form to the word's meaning. You should already know that the figure does not correspond to everyone's view of what word meaning is because what I'm calling the "semantic category" could be distributed in various ways rather than localized as it appears here.

How words change

What happens when there is a new category that we need a word for? One possibility is to invent an entirely new word, but this apparently doesn't happen so often. More often the meaning of an existing word is extended to include the new category. When meaning is extended, this is done on the basis of some kind of relationship between the old meaning and the new. I will refer to this as a conceptual relation. The general situation involved in extending the meaning of a word, semantic extension, is shown in the figure below.

Let's see how semantic extension might work for our Lexies. Say they are familiar with domestic cats and have a word for them; for simplicity, let's say it's pronounced like the English word cat. Now they discover tigers and leopards. Each of these new categories gets its own noun, but in becoming familiar with these new animals, the Lexies see their similarities with domestic cats and develop a new category that encompasses all three categories of animals. How do they refer to this new category, that is, to the more general category of cats, what zoologists refer to as members of the family Felidae? (For simplicity, I'll call this category general-cat.) One possibility, which is the one used by many English speakers, is to refer to this category using the same word that is used for its most familiar sub-category, that is, cat. Note that the word cat now has two related meanings. I will refer to related meanings of a single word as word senses. For a word that has more than one sense, it is up to the Hearer to figure out when the word is used which of the senses is intended by the Speaker.

Here is another English example of a word with multiple senses. The noun chicken can refer both to a particular kind of bird (an object) and to a kind of meat made from this bird (a mass). Notice the two senses in the following sentences.

  1. There's a chicken walking around in the back yard.
  2. There's some chicken in the freezer.

The discussion so far might make it seem that language users, or entire language communities, extend the meanings of words consciously, but this rarely happens. Instead there seems to be a natural process by which the meanings of words change over time. As with other kinds of language change, the details of the process are not well understood. Somehow a change that starts with a small number of Speakers has to spread throughout the community and become conventional.

Generalization, specialization, and taxonomies

A baby uses the word truck for cars and buses as well as trucks. How would you describe this error? How is it like a semantic extension? He also uses the word train only for the toy train he plays with. How is this kind of error different from the first?

The extension of cat to include a new sense seems reasonable because the two senses are closely related. In this subsection, we'll examine this particular conceptual relation in more detail.

Every domestic cat is a member of the cat family (Felidae), that is, an instance of the category general-cat. Every tiger and every leopard is also an instance of this category. All of the properties that characterize the category general-cat, in particular, a characteristic body shape and way of moving, characterize domestic cats, tigers, and leopards. I will refer to the conceptual relation between the categories domestic-cat and general-cat as specialization-generalization. General-cat generalizes domestic-cat; domestic-cat specializes general-cat.

One way knowledge of objects is organized in long-term memory

There is evidence from cognitive science that much of what we know about objects is organized in terms of the specialization-generalization relation. This is especially true for living things, for which we seem to represent the categories in the world in taxonomieswikipedia with multiple levels for different degrees of generality. Here is a possible portion of a taxonomy representing knowledge of animals. There are three points to be mentioned about the figure, and about conceptual taxonomies in general.

  • As indicated by the small capitals, this is meant to represent a taxonomy of concepts, potential meanings of words, not a taxonomy of words.
  • Such a taxonomy is a psychological entity; it represents the way some person might organize their knowledge about the world, not a scientific account of what is actually in the world. As you may know, zoologists would include several more levels in their scientific taxonomy for animals.
  • As before, we need to be careful about taking the boxes too seriously since there are theories of categories that get by without anything so localized.

cat taxonomy

As we go higher in the figure, the categories become more general; there are fewer and fewer features that characterize their instances. Thus we can say a great deal about the characteristic sounds made by domestic cats, much less about the characteristic sounds made by members of the cat family, even less about the characteristic sounds made by mammals.

Here is another example, representing how someone might organize their knowledge about fruits.

Again there are fewer and fewer characteristic properties of the categories as we go higher in the taxonomy. Apples have a characteristic smell that resembles the smell of pears but is not characteristic of the smell of fruits in general.

If you're familiar with an object-oriented programming language such as Java, Python, or C++, this should all appear familiar to you. Taxonomies like those illustrated in the two figures are inheritance hierarchies,wikipedia with the nodes in the trees corresponding to the classes of object-oriented programming. This relationship brings up the question of how we should implement knowledge of this sort in a program that's designed to simulate human processing of words or to be a component of a practical system that interacts with users. There are two possibilities. We can use object orientation to directly implement the taxonomy, creating explicit classes for Food, Fruit, Berry, etc., and using the inheritance mechanisms that are built into the language itself to make use of the knowledge that is shared. Or we can treat each category in the taxonomy as an object, an instance of a class like Concept and write procedures to implement inheritance bewteen these objects. Most researchers have followed the second path, in part because it gives them control over how inheritance works, how and when new categories are created and associated with the existing taxonomy. But further consideration of these implementation issues is beyond the scope of this book.

What does all of this have to do with words? First, as we have seen from the example of cat, words may extend their meanings on the basis of the generalization relation. The noun cat came to mean not only domestic-cat, but also general-cat. The figure below illustrates this process.

The opposite is also possible; a word may take on a sense that is more specific than its original sense. Consider the following example from the history of English. In Middle English the world gerol meant 'young person'. Over time the meaning of the word shifted to 'young female person', which is the sense it has in in its present form, girl. This is shown in the figure below, which illustrates the situation after the meaning had changed. The new sense was a specialization of the original sense. Notice that in this case, unlike what happened with cat in our first example, the original sense was lost after the word took on the new sense.

Generalization and specialization in the borrowing of words

A similar process may occur when a word is borrowed from one language into another; the sense of the word in the source language may be generalized or specialized after the word enters the target language. The usual Tzeltal word for 'person' is kirsiano (the exact pronunciation depending on the dialect), borrowed from the Spanish word cristiano meaning 'Christian'. For whatever reason, in the borrowing process the meaning was generalized from 'Christian person' to (any) 'person'. The Swahiliwikipedia word safari means 'trip', but when this word was borrowed into English from Swahili, it took on the special sense of a 'trip in search of game animals'. In this case, the meaning was specialized when the word was borrowed.

There are also many examples of generalization and specialization in the speech of young children. In this case we can think of the adult sense of the word as basic and the children's extension of this as a second sense, though it may not be clear that the child has learned the adult sense. Because these uses are seen as errors from the perspective of the adult model, they are referred to as over-generalization and under-generalization. An example of over-generalization is the use of dog to refer to other mammals roughly the size of dogs such as goats in addition to dogs. Examples of under-generalization are harder to observe because they require noticing that the child fails to use a word for a referent where an adult would use the word. An example would be the use of dog to refer only to a particular dog.

These errors made by children are interesting because they point up the possible similarity between the mechanism of language change and the mechanisms of language learning. What we see in the history of a language, the result of changes across an entire community, possibly over the course of multiple generations, resembles what we see in the development of a single child's linguistic system. We'll see more such examples in the book later on. The similarity implies that we might be able to understand language change as a process of learning taking place in the minds of many different language users, children and adults.

Concepts without words (again)

Finally, notice that there may be categories in a person's taxonomy that the person has no words for. Look at how the fruit taxonomy in the figure above corresponds to words for a particular English speaker (me).

apple taxonomy 2

While I have a category for things that are either apples or pears, that is, I recognize the similarities between apples and pears, I don't have a word for this category. Note that this does not imply that there is no word in the language for this category; botanists call the family that includes pears and apples Pomoideae. But I had never heard this word before I looked it up in order to mention it here, so it is (or was) not a part of my mental lexicon. Because I have words for all or most of the other categories in this taxonomy, we can consider the apple/pear category to constitute a lexical gap for me. We will see other examples of lexical gaps later in this chapter.


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