Prototype Theory Research Paper

There is another way in which categorization impinges on linguistic theory. The moment one pursues even the most elementary linguistic analysis, language itself becomes an object of categorization. Like any intellectual discipline, linguistics requires its practitioners to set up categories for the description of the object of study. In any linguistic description, one will encounter such entities as words and morphemes, phrases and clauses, nouns and verbs, subjects and objects, clitics and particles, phonemes and allophones. ‘Doing linguistics’ consists, in large measure, in setting up categories such as these, defining them, studying their properties and interrelationships, working out criteria for determining their membership, and applying them to the data at hand. The ontological status of the categories themselves may also become an issue. Where do categories such as ‘noun’ and ‘verb’ come from? Are they inherent in the object of study? Are they mere descriptive conveniences? Are they constructs of linguistic theory?

1. Two Approaches To Categorization

Two major approaches to categorization are the ‘classical’ approach and the ‘prototype’ approach. On the classical approach, a category is defined in terms of a set of necessary and sufficient conditions for category membership. The set of conditions specifies the essence, as it were, of the category. Any entity meeting all the conditions is, by definition, a member of the category; failure to meet any of the conditions excludes an entity from the category. On this view, category boundaries are discrete (an entity either is, or is not, a member), and the category lacks internal structure (all members are of equal status).

The simplicity of the classical view makes it intuitively appealing. A major problem is that many categories are simply not amenable to classical definition. What, for example, are the defining features of ‘chair,’ ‘vegetable,’ and ‘love,’ or, for that matter, of ‘cup,’ ‘saucer,’ and ‘in’? In fact, classical categorization probably works best only for ‘expert’ categories, that is, categories that have been created and explicitly defined (in classical terms!) by experts, whether these be scientists, bureaucrats, administrators, or whoever. For most words of everyday speech, the classical theory is quite inappropriate.

On the prototype approach, a category is understood, primarily, in terms of its good examples. Entities are associated with the category to the extent that they resemble the good examples. Often, the boundary of a prototype category will be fuzzy—it might not be clear whether some entities belong in the category or not. Moreover, prototype categories have an internal structure, in that some entities count as more central members than others.

Prototype categorization came to the attention of linguists largely due to the work of the psychologist, Eleanor Rosch. In a series of experiments, summarized in Rosch (1978), it emerged that the meanings of several very ordinary words, such as bird, toy, ehicle, are structured around good examples. People readily agree that a robin is a better example of ‘bird’ than a penguin; they can determine the truth of A robin is a bird faster than A penguin is a bird; when asked to name members of a category, they name more central examples before more marginal examples; and when drawing inferences about a category, people tend to draw on knowledge of central members, rather than on knowledge about the category as a whole. Rosch observed prototype effects both with ‘natural kind’ categories—that is, categories such as ‘bird,’ which are, as it were, given by nature—and with categories that are understood relative to human concerns, such as ‘vehicle,’ ‘furniture,’ and ‘toy.’

Rosch’s discoveries were eagerly taken up by linguists, and extended by a wide range of linguistic data (Lakoff 1987, Kleiber 1990, Tsohatzidis 1990, Geeraerts et al. 1994, Taylor 1995). An especially fruitful application has been the study of semantic change (Geeraerts 1997). The prototype notion has also been widely applied to the study of the categories of linguistic description (Langacker 1987), Croft 1991).

2. Problems And Refinements

Despite its success in lexical semantics and elsewhere, prototype categorization raises a number of problems.

While not denying the reality of prototype effects, Fodor (1996) argues that concepts cannot be equated with prototypes. The fish prototype (a herring?) and the pet prototype (a poodle?) contribute nothing at all to the complex concept ‘pet fish,’ nor to the prototype of ‘pet fish’ (a goldfish?). Generally, as a concept gets specified in greater detail, prototype effects not only shift, they also tend to get effaced. Consider the diminishing role of the ‘nurse’ prototype in one’s understanding of nurse, male nurse, retired male nurse, etc. On the other hand, prototype effects show up even on categories that arguably are subject to classical definition, such as ‘odd number.’ Armstrong et al. (1983) report that subjects readily agreed that 3 was a better example of ‘odd number’ than 447, even though, obviously, 447 is no less of an odd number than 3.

On one interpretation of these findings, prototype effects are extrinsic to word meanings as such, and arise only when a person applies a concept to the world. This view draws a distinction between the ‘essence’ of a category (the ‘real’ meaning of a word), and ‘recognition procedures’ invoked when speakers attempt to categorize things and eventualities in the world. On this view, the fuzziness of category boundaries results from the fact that eventualities in the world may not lend themselves to clear-cut categorization, even though the words of a language do have clear-cut meanings. Although it might not be clear whether a particular utterance counts as a ‘lie,’ the meaning of lie might nevertheless be clear-cut.

2.1 Degree Of Membership vs. Representativity

Before endorsing this exclusion of prototypes from word meaning proper, it is important to distinguish two aspects of prototype categories: fuzziness of category boundaries (a question of category membership), and degree of representativity within a category (a question of category structure).

It is uncontroversial that certain categories are inherently fuzzy, in that it is simply not possible to make a clean distinction between what goes into the category and what does not. This is the case with many adjectival concepts, such as ‘old,’ ‘tall,’ and ‘bald.’ While there is little doubt what a ( prototypical) bald head looks like, also what it means to be not bald, it would be futile to draw a boundary between ‘bald’ and ‘not bald,’ e.g., in terms of the number of hairs on a person’s head.

However, prototype effects also show up on categories that arguably do have clear boundaries. Although turkeys might not be good examples of the bird category, they are birds nonetheless, albeit not very representative ones. Representativity, to be sure, can be understood in different ways—in terms of frequency of occurrence, cultural or environmental salience, or statistical averaging over category instances. Representative examples are typically invoked in default contexts. Given only the mention of ‘a bird,’ with no further specification, one would assume a representative example. A person who wishes they were a bird would surely be disappointed if they were transformed into a turkey! The internal structure of a category cannot reasonably be excluded from a person’s knowledge of word meanings.

2.2 Prototypes And Background Knowledge

Categories, in order to be viable, need to be conceptually coherent (Murphy and Medin 1985). A category is coherent to the extent that it is based on theories of how the world is, and how it links up with a person’s encyclopedic knowledge. A category is not simply a conjunction of an ad hoc set of features, the category has to make sense.

Lakoff (1987) discusses this aspect in terms of his notion of the Idealized Cognitive Model (ICM). The concept ‘bachelor’ is understood against an ICM of marriage practices (which in turn is based in ICM’s of sexuality, procreation, and family). One aspect of the ICM is the idea that each person, after reaching the ‘marriageable age,’ sooner or later marries. Within the ICM, bachelor may well be definable in classical-like terms, i.e., as ‘unmarried,’ ‘adult,’ and ‘male.’ Prototype effects arise, because the ICM may not fit the world perfectly. The Pope is not a good example of ‘bachelor,’ not because of uncertainties about whether the Pope is unmarried, adult, or male, but because Catholic clergy are outside the scope of the ICM.

2.3 Prototypes And Features

On the classical theory, categories are assembled, as it were, out of their features; the features pre-exist the category, they are evaluated independently of the category, and must be simpler than the category they define. A prototype, in contrast, can be perceived holistically, as a gestalt; features are no longer the building blocks of categories, they emerge, as dimensions of similarity, through acquaintance with cat egory members. It is unlikely that people construct their bird-category through conjunction of features such as ‘having feathers’ and ‘laying eggs’; knowledge of feathers and egg-laying emerges from acquaintance with birds, not vice versa. Likewise with linguistic categories. One might propose that ability to inflect for tense is a defining characteristic of verbs (for English, at least). Yet, the very notion of tense inflection rests on a prior acquaintance with members of the verb category.

Given this revised understanding of features, a feature-based view of prototype categories becomes possible, through the differential weighting of the features. Some features may be better cues to category membership than others; some features may be virtually indispensable; others are able to be overridden. The prototype will be a representation that maximizes feature weights; an entity exhibiting highly weighted features will automatically count as a category member; an entity exhibiting less highly weighted features might still count as a member, though a more marginal one. Moreover, it is possible for two entities to belong to a category, even though they have no categoryspecific features in common. The way also opens up for a reconciliation of classical and prototype categorization—a classical category is the limiting case of a prototype category, i.e., a category understood solely in terms of essential features.

3. Prototypes And Polysemy

It is useful to distinguish between the prototype structure of a concept and the polysemy structure of a word. There is a clear difference, in principle, between applying the word fruit to different kinds of fruit, and the use of the word in such expressions as the fruit of his labors. The latter usage represents a semantic extension of the word, in a way that is different from the use of the word to refer, say, to olives.

Take the preposition over (Lakoff 1987). Fly over the Atlantic, the lamp hanging over the table, put your hands over your face, come over here, there’s water all over the floor, the party’s over, do it over again—these exemplify different senses of the word, rather than more or less representative examples of one and the same sense. To the extent that these senses can be clearly individuated, it is possible to construct a network of sense relations, which links up the different senses according to their similarity. Such an array invites a prototype analysis, with one of the senses selected as central, and the others radiating out from it.

There are, however, different criteria for selecting the central sense, and these do not always deliver the same result. On a diachronic perspective, the basic sense is the historically oldest one, from which the others have been derived over time. On a developmental perspective, the basic sense is the one that children acquire first. Alternatively, the descriptive linguist (or lexicographer) might select as basic the most frequent sense, or the one to which the others can be most economically related. The real question, however, concerns the speaker’s mental organization of polysemy. Currently, this is a lively topic in polysemy research (Taylor 1995).

4. Prototypes And Linguistic Categories

The prototype concept may be applied, not only to the study of word meanings, but to the very categories of linguistic description. Many linguistic concepts (including the very notion of ‘language’ and ‘a language’) turn out to have a prototype structure, in that they exhibit degrees of representativity, and often have fuzzy boundaries. Uncertainty as to what goes into a category and what does not pertains even to such basic notions as what constitutes a word (as opposed to a bound morpheme, clitic, or phrase), the part-of-speech categories (whether a particular item is a noun, verb, adjective, etc.), constituency (whether a particular string of words is a syntactic constituent), and syntactic relations (whether a particular constituent is a modifier or adjunct, the subject of a clause, or whatever).

Some linguistic theories propose to decide such issues by fiat. In practice, however, the linguist’s strategy often reflects a prototype conception, even though this might not be explicitly acknowledged. When deciding the category status of a linguistic item, it is usual to apply a set of tests (Croft 1991). The tests are set up on the basis of what, intuitively, count as good examples of the category in question, whereby each of the tests diagnoses a property typical of the good examples. An item which passes all the tests is ipso facto a member of the category; an item which fails the tests is not a member. Sometimes, an item passes only some of the tests; it will have to be regarded as a marginal example, or even as an item of uncertain status.

Consider the parts of speech, perhaps better called ‘lexical categories,’ such as ‘noun,’ ‘verb,’ ‘adjective,’ ‘preposition.’ These can be characterized either in semantic or in formal terms. Semantically, nouns prototypically designate categories of things, i.e., concrete, time-stable, spatially bounded objects (chain, cup, etc.); verbs designate events, involving rapid changes in state (explore, arrive); adjectives designate fairly stable properties of things (hot, young); while prepositions designate a relation, typically a spatial relation, between things (on, at). It is commonly agreed that lexical category cannot be reliably predicted from a word’s semantics. In spite of their reference to rapid changes in state, explosion and arrival are nouns, just as good nouns, in fact, as chair and cup. This is because the words exhibit the full range of formal properties typical of the noun category, i.e., they pass all the syntactic tests for nounhood—they pluralize, they take the full range of determiners, they can be modified by an adjective, they can head a subject noun phrase, and so on. There are words which fail to exhibit the full range of properties. Groceries, in I bought some groceries, looks like the plural of a noun grocery—yet there is no such noun (*I bought a grocery), neither can groceries take numeral quantifiers (*fi e groceries). Syntactically, groceries is a somewhat marginal noun (though still a noun). However, there are words whose status is genuinely unclear. Consider saying, in without my saying a word. Being the complement of a preposition, my saying a word looks like a noun phrase, headed by saying, and saying looks like a noun, in that it takes possessive my. Other determiners, though, are not possible (without *the *that *a saying a word ). Moreover, saying is followed by what looks like a direct object (a word ), and the ability to take a direct object is a distinctly verb-like property, not at all a property of nouns.

Both semantic and formal criteria, then, fail to deliver clear-cut lexical categories. Nevertheless, there is an important sense in which the semantic prototypes have priority. Any language has to provide its speakers with the means to refer to ‘things’ and ‘events,’ ‘properties’ and ‘relations,’ and the semantic prototypes of the lexical categories, in English and other languages, are understood in such terms. Indeed, without the semantic prototypes, there would be no basis for recognizing the categories ‘noun’ and ‘verb’ across the different languages of the world.

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