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This article is about . For , see Definition (disambiguation).

A definition may be a statement of the essential properties of a certain thing, or a statement of equivalence between one expression and another, usually more complex expression that gives the meaning of the first. These two senses are not mutually exclusive, nor are they equivalent.

A thing being defined is called (from Latin) a definiendum; the expression which defines it is called a definiens.

Kinds of definition

A number of different kinds and techniques of definition can be distinguished, including:

  • A dictionary definition or lexical definition reports the meaning of word or expression as it is normally used, usually by supplying an (approximately) equivalent expression in which the original word does not occur. For example, bachelor might be defined as an unmarried man; and fry as to cook in hot oil. (Notice the addition of "an" and "to" in each case, so that the defining expression is not perfectly inter-substitutable with the original: You can say John is a bachelor, but not John is a an unmarried man. This is normal practice, and is done simply for ease of reading.) With some words, like the and if, which cannot be effectively paraphrased, dictionaries will often describe their proper use without offering an equivalent expression.
  • Contextual definition Some words cannot be clearly defined on their own, but it is possible to offer a schema for defining every sentence in which they occur--that is, a way of replacing every sentence containing the expression with another sentence not containing the expression. Russell's famous Theory of Descriptions was an attempt (now widely believed to be incorrect) to do this for all definite descriptions—expressions of the form the (unique) x. On Russell's account, any sentence containing (for example) the expression "the present king of France" was to be rearranged like this: The present king of France is bald means There is exactly one thing which is currently a king of France, and that thing is bald. Notice that the defined expression, a noun phrase, is replaced by a sentence (There is . . . France) and a noun phrase (that thing) which appears in the position of the original.
  • An intensional definition specifies all and only the properties required of something in order that falls under the term defined (its necessary and sufficient conditions). This, like the following is typically used to characterize ways of specifying sets. For example, the set of primes less than 20, or {x:x is prime and x < 20}, is an intensional definition of a set.
  • An extensional definition lists everything that the defined term actually applies to (its extension). Like the above, this is often used in charactizing definitions of sets: {2, 3, 5, 7, 11, 13, 17, 19} is an extensional definition of the same set as mentioned there. Note that extensional definitions cannot be used to specify infinite sets (all the prime numbers, say). They are also not counterfactually robust: If you "define" dog by making a list of all the dogs, then you will not have any grounds for deciding whether some newly encountered animal would be a dog.
  • An ostensive definition gives the meaning of a term by pointing out the thing denoted by it, or pointing out examples of the kind of thing meant by it. So you can explain who Jones is by pointing him out to me; or what a dog is by pointing at several and expecting me to "catch on."
  • A definition by genus and difference "is one in which a word or concept that indicates a species -- a specific type of item, not necessarily a biological category -- is described first by a broader category, the genus, then distinguished from other items in that category by differentia."
  • A recursive definition or inductive definition is one which defines a word in terms of itself, so to speak, albeit in a useful way. Normally this consists of two (or three) steps: (I) Several specific objects (a "base set") are stated to fall under the term X being described. (II) All and only the things bearing a certain relation to members of X are also stated to be members of X. For instance, we could define natural number as folows: (I) 1 is a natural number. (II) The successor of a natural number is also a natural number, and nothing else is. ("Nothing else is", the closure step, is sometimes considered a separate step.) For this to work well, the definition in any given case must be well-founded, avoiding a circle or an infinite regress. (See the following.)
  • A circular definition is one that assumes a prior understanding of the term being defined. For instance, we can define "oak" as a tree which has catkins and grows from an acorn, and then define "acorn" as the nut produced by an oak tree. To someone not knowing either which trees are oaks or which nuts are acorns, the definition is usually fairly useless. (see tautology)
  • A stipulative definition is the specification of a meaning adopted or assumed specifically for the purposes of argument or discussion in a given context. For example, I might want to explain to you how beer is made, but not be sure whether sake is a kind of beer nor how to is made. So I might stipulate at the beginning that By "beer" I mean only beer brewed from barley.
  • A precising definition "is a definition that extends the dictionary definition (lexical definition) of a term for a specific purpose by including additional criteria that narrow down the set of things meeting the definition."
  • A persuasive definition "is a type of definition in which a term is defined in such a way as to be an argument for a particular position (as opposed to a lexical definition, which aims to be neutral to all usages), and is deceptive in that it has the surface form of a dictionary definition."

Determining meaning: extension, intension, ambiguity, and vagueness

Just as arguments can be good or bad, definitions can be good or bad. A definition gives us the meaning of a word. To understand this more deeply requires an elucidation of a few features of meaning, the principal ones being extension, intension, ambiguity, and vagueness.

The distinction between the extension and the intension of a word is very similar to the distinction between a word's denotation and connotation. For example, the extension of the word "bachelor" would be all and only the bachelors in the world. The extension of this word would include several hundreds of millions of men. The intension of the word is more brief because it includes just two properties: the property of being a man, and the property of being unmarried. Essentially, all bachelors are unmarried men, and only bachelors are unmarried men.

The sort of definition that philosophers are interested in, insofar as they are interested in definitions at all, is one that identifies a word's intension, rather than its extension. A definition of the word 'bachelor' is 'unmarried man' which could also be specified by a very long list including all unmarried men. Aside from being practically impossible, such a list is not what is generally desired. What is desired is a description of what all those things we call 'bachelors' have in common that distinguishes them from all non-bachelors. A list of all bachelors would be static, and could not expand to determine whether any new human is a bachelor or not.

There are two different ways in which the meanings of words can be unclear. Words can be unclear in the sense of being ambiguous, of being vague, or a combination of the two. Most words are, in fact, both ambiguous and vague. This is not a skeptical or even a controversial claim; to say that many, or perhaps even most, words are both ambiguous and vague is not to say that they have no meaning. It is to say, first, that many individual words have many distinct senses; and, second, that those senses are often, in ordinary language, not meant to be exhaustively precise. A word that is both ambiguous and vague, whose extreme limits are fuzzy and undefined, can still contain a rich fund of meaning.

A definition of 'definition'

Suppose we have decided to define a certain word or a concept associated with that word. Suppose also that we have identified which sense of the word we are interested in, and we have noted clear cases, some unclear cases, and some borderline cases of the application of the word. The question then is: how can this word be defined? What is desired here is a description of the intension of the word: that is, an account of the set of properties that characterizes all and only members of the extension. In that case, it seems the following is a serviceable account of the meaning of '(intensional) definition':

The definition of a concept, or of (a given sense of) a word or phrase, is a description of its intension—that is, the set of properties that characterizes all and only members of the extension of the word; the extension is all the things that the concept, word, or phrase applies to.

Some philosophers have criticisms of this sort of definition of the word definition; or perhaps it would be better to say that some philosophers think that it is, for various reasons, impossible to give exhaustively exact definitions of most concepts, words, and phrases. Two prominent critics are Wittgenstein and Quine. Still most philosophers acknowledge that in philosophy something similar to giving definitions of important philosophical concepts is necessary.


"Nothing is more usual than for philosophers to encroach on the province of grammarians, and to engage in disputes of words, while they imagine they are handling controversies of the deepest importance and concern."David Hume

See also

Look up definition in Wiktionary, the free dictionary.

External links

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