The Definitional and Prototype Theories of Meaning

by Gleitman, Reisberg, & Gross

“Word meanings are of many different kinds. Some words such as ‘Aristotle’ and ‘Santa’ describe individuals in the real and imaginary world; others such as ‘dog’ and ‘unicorn’ are more general and describe categories of things. Yet other words describe substances (‘water’, ‘aether’), properties (‘blue’, ‘imaginary’), relations (‘similar’, ‘father’), quantities (‘some’, ‘zillions’), actions (‘run’, ‘transform’), states of mind (‘knowing’, ‘hoping’), or being (‘am’, ‘seem’), and manners of doing (‘carefully’, ‘musically’). A moment’s thought reveals that the kind of meaning is well correlated with the so-called parts of speech, with things and stuff generally labeled by nouns, acts and states by verbs, properties by adjectives, and manners by adverbs.”

This is reminiscent of “Like everything metaphysical, the harmony between thought and reality is to be found in the grammar of language.” [Wittgenstein]


“At first glance, the words of a language seemed to be like little atoms of meaning, each distinct from all the others, but several theories of word meaning assert that only a handful of words in the language describe elementary, ‘simple’ ideas or concepts. The rest are more like molecules―they’re composed of more elementary atoms of meaning. Thus, words like ‘yellow’ and ‘round’ may indeed name simple ideas or concepts, but other words seem more complex―for example, the words ‘canary,’ ‘yolk’, and ‘banana’ all seem to involve the atom of ‘yellowness’, but they involve other elements as well.”

“These observations are central to the definitional theory of word meaning, which states that words are organized in our mind much as they are in standard dictionaries (though not in alphabetical order). According to this theory, each word can be understood as a bundle of meaning atoms. The full meaning of each word is a set of features that are essential for membership in the class named by the word. Thus, ‘bachelor’ is composed of the set of features [single], [human], [adult], and [male]. These features are necessary for bachelorhood, and so, if some creature is missing any of these features (e.g. if the creature is married or is an adult male duck) it couldn’t correctly be called ‘a bachelor’. And this set of features is also sufficient for bachelorhood―some man might be tall or short, flirtatious or shy, English or Greek, but none of this affects his status as a bachelor.”

“The definitional theory of meaning faces several problems. For one thing, once we’ve gone beyond such relatively formal words as ‘bachelor’, it’s surprisingly hard to come up with definitions that cover all the uses of a word or do it justice at all. For instance, consider the proposed definition of bird: ‘Any of a class of warm-blooded vertebrates distinguished by having the body more or less completely covered with feathers and the forelimbs modified as wings.’ This definition seems promising, but, in fact, not all birds are covered with feathers (neither baby birds nor plucked birds have feathers, yet they’re still birds all the same).”

This is an instance of what I imagine Dennett had in mind when he said, “As is so often the case, it’s easier to give examples than to give a definition of the term.”

“A related problem for the definitional theory is that some members of a meaning category appear to exemplify that category better than others do. Thus, a German Shepherd seems to be a more typical dog than a Pekinese, and an armchair seems to be a better example of the concept of furniture than a reading lamp. This seems to be at odds with the analysis we’ve described thus far, whose aim is to specify the necessary and sufficient attributes that define a concept.”


“Observations like these have led some investigators to argue for an alternative view, called the prototype theory of meaning. The facts that prototype theory tries to account for can easily be illustrated. Consider again the category ‘bird’. Are there features that characterize all birds and that characterized birds only? One might think that being able to fly is a feature of all birds, but it’s not―ostriches can’t fly. One might suppose that having feathers is a feature of all birds, but as we’ve noted, it’s not. And not everything that lays eggs, flies, or has feathers is a bird. With all these failures of the definition in mind, perhaps it’s wrong to suppose that we can ever find a set of necessary and sufficient features or the concept ‘bird’. But if not, then the definitional theory isn’t correct.”

“According to prototype theory, the meaning of many words is still described as a set of features, but not a necessary and sufficient set of them. Instead, the concept is held together in a family resemblance structure (Wittgenstein). (My psychology textbook actually cited Wittgenstein here.) Consider the ways that members of a family resemble each other. Joe may look like his father to the extent that he has his eyes, and he may look like his mother by virtue of his prominent chin. His sister Sue may look like her father to the extent that she has his nose, and she may smile just like her mother. But Joe and Sue may have no features in common, and so the two of them don’t look alike at all. Even so, they’re both easily recognized as members of the family, for they each bear some resemblance to their parents. Some members of the family may have more of these features than others do. Accordingly, some members of a category seem more typical or central than others. Thus, a German Shepherd seems ‘doggy-er’ than a Pekinese, presumably because the Shepherd has more of the features associated with the dog family.”

“How is knowledge about a family resemblance structure represented in the mind? According to some psychologists, we carry in memory a mental prototype for each of our concepts―a prototypical bird, a prototypical chair, and so on. These prototypes are generally derived from our experiences, so that each prototype provides something like a mental average of all the examples of the concept we’ve encountered. A sparrow resembles it in many ways and so is judged to be a ‘good’ bird; a penguin resembles it just a little and hence is a marginal bird; a rock doesn’t resemble it at all and hence is judged not to be a bird.”


“The prototype theory helps us to understand why robins are perceived to be more typical birds than ostriches. But the definitional theory explains why an ostrich is nevertheless recognized as a bird. The prototype theory helps us understand why a trout is fishier than a seahorse, but the definitional theory seems important if we’re to explain why a seahorse is far fishier than a whale (which, of course, isn’t a fish at all, though it has some suspiciously fishy properties). Perhaps we can combine both theories of meaning rather than choosing between them.

Consider the word ‘grandmother’. For this term, there are necessary and sufficient features, so here the definitional theory seems just right: a grandmother is a female parent of a parent. But there may also be a prototype: a grandmotherly grandmother is a person who is old and grey, has a kindly twinkle in her eye, and bakes cookies. When we say that someone is ‘grandmotherly’, we’re surely referring to the prototypical attributes of grandmothers, not to genealogy. And in many circumstances, we use this prototype, rather than the definition. For example, we’re likely to rely on our grandmother prototype for picking a grandmother out of a crowd, for predicting what someone’s grandmother will be like, and so on. But in other circumstances, we rely on the definition: if we know some kindly lady who is grey and twinkly but never had a child, we may think of her as grandmotherly but not as a grandmother.

It appears, therefore, that people may have two partly independent mental representations of ‘grandmother’, and the same may be true for most other words as well.”


“Category-membership for concepts in the human brain is not a yes/no affair, as the necessary and sufficient conditions approach of the classical view assumes. Instead, category membership is fuzzy.” [1]

“The idea of necessary and sufficient conditions is almost never met in categories of naturally occurring things.” [2]

“Psychologists studying the nature of concepts and categorization of judgments have been pushed to abandon the view that we represent concepts with simple sets of necessary and sufficient conditions. The data seem to show that, except for some mathematical and geometrical concepts, it’s not possible to use simple sets of conditions to capture the intuitive judgments people make.” [3]



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