For alternative meanings see definition (disambiguation)

A definition may be a statement of the essential properties of a certain thing, or a statement of equivalence between a term and that term's meaning. The two are not mutually exclusive, nor are they equivalent.

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

  • Intensional definition "gives the meaning of a term by giving all the properties required of something that falls under that definition; the necessary and sufficient conditions for belonging to the set being defined."
  • Extensional definition "gives the meaning of a term by listing everything in its extension -- that is, everything that falls under that definition."
  • Ostensive definition "conveys the meaning of a term by pointing out examples of what is defined by it. "
  • 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."
  • Circular definition "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 fairly useless." (see tautology)
  • A recursive definition is one which defines a word in terms of itself, albeit in a useful way. For that to work, the definition in any given case must be well founded, avoiding an infinite regress. For instance, we could define natural number as "1 or the successor of a natural number".
  • Stipulative definition occurs when "a new or currently-existing term is given a new meaning for the purposes of argument or discussion in a given context."
  • 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."
  • 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 still 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

External links

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