Type–token distinction
Encyclopedia
In disciplines such as philosophy
and knowledge representation
, the type-token distinction is a distinction that separates an abstract
concept
from the objects
which are particular instances of the concept. For example, the particular bicycle in your garage is a token of the type of thing known as "The bicycle." Whereas, the bicycle in your garage is in a particular place at a particular time, that is not true of "the bicycle" as used in the sentence: "The bicycle has become more popular recently." In logic
, the distinction is used to clarify the meaning of symbol
s of formal language
s.
Types are often understood ontologically
as being abstract objects. They do not exist anywhere in particular because they are not physical objects. Types may have many tokens. However, types are not directly producible as tokens are. You may, for instance, show someone the bicycle in your garage, but you cannot show someone "The bicycle." Tokens always exist at a particular place and time and may be shown to exist as a concrete physical object.
It can be quite useful to distinguish between an abstract "type" of thing, and the various physical "tokens" or examples of that thing. This type-token distinction is illustrated by way of examples. If we say that two people "have the same car", we may mean that they have the same type of car (e.g. the same brand and model), or the same particular token of the car (e.g. they share a single vehicle). This distinction is useful in other ways, during discussion of language. In the phrase "Grendel is Grendel is Grendel is Grendel", there are only two types of words ("Grendel" and "is") but there are seven tokens (four "Grendel" and three "is" tokens).
discovered this distinction, however only gave what he called an "artificial, but convenient and adequate definition" as "an occurrence of x in y is an initial segment of y ending in x."
If we consider for example the famous sentence: "A rose is a rose is a rose." We may equally correctly state that there are eight or three words in the sentence. There are, in fact, three word types in the sentence: "rose", "is" and "a." However, although there are eight word tokens in a token copy of the line, there aren't any tokens at all in the line itself. The line itself is a type. There are not eight word types in the line. It contains (as stated) only the three word types, ‘a,’ ‘is’ and ‘rose,’ each of which is unique. So what do we call what there are eight of? They are occurrences of words. There are three occurrences of the word type ‘a,’ two of ‘is’ and three of ‘rose’.
The need to distinguish tokens of types from occurrences of types arises, not just in linguistics, but whenever types of things have other types of things occurring in them.
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...
and knowledge representation
Knowledge representation
Knowledge representation is an area of artificial intelligence research aimed at representing knowledge in symbols to facilitate inferencing from those knowledge elements, creating new elements of knowledge...
, the type-token distinction is a distinction that separates an abstract
Abstraction
Abstraction is a process by which higher concepts are derived from the usage and classification of literal concepts, first principles, or other methods....
concept
Concept
The word concept is used in ordinary language as well as in almost all academic disciplines. Particularly in philosophy, psychology and cognitive sciences the term is much used and much discussed. WordNet defines concept: "conception, construct ". However, the meaning of the term concept is much...
from the objects
Object (philosophy)
An object in philosophy is a technical term often used in contrast to the term subject. Consciousness is a state of cognition that includes the subject, which can never be doubted as only it can be the one who doubts, and some object or objects that may or may not have real existence without...
which are particular instances of the concept. For example, the particular bicycle in your garage is a token of the type of thing known as "The bicycle." Whereas, the bicycle in your garage is in a particular place at a particular time, that is not true of "the bicycle" as used in the sentence: "The bicycle has become more popular recently." In logic
Logic
In philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...
, the distinction is used to clarify the meaning of symbol
Symbol (formal)
For other uses see Symbol In logic, symbols build literal utility to illustrate ideas. A symbol is an abstraction, tokens of which may be marks or a configuration of marks which form a particular pattern...
s of formal language
Formal language
A formal language is a set of words—that is, finite strings of letters, symbols, or tokens that are defined in the language. The set from which these letters are taken is the alphabet over which the language is defined. A formal language is often defined by means of a formal grammar...
s.
Types are often understood ontologically
Ontology
Ontology is the philosophical study of the nature of being, existence or reality as such, as well as the basic categories of being and their relations...
as being abstract objects. They do not exist anywhere in particular because they are not physical objects. Types may have many tokens. However, types are not directly producible as tokens are. You may, for instance, show someone the bicycle in your garage, but you cannot show someone "The bicycle." Tokens always exist at a particular place and time and may be shown to exist as a concrete physical object.
It can be quite useful to distinguish between an abstract "type" of thing, and the various physical "tokens" or examples of that thing. This type-token distinction is illustrated by way of examples. If we say that two people "have the same car", we may mean that they have the same type of car (e.g. the same brand and model), or the same particular token of the car (e.g. they share a single vehicle). This distinction is useful in other ways, during discussion of language. In the phrase "Grendel is Grendel is Grendel is Grendel", there are only two types of words ("Grendel" and "is") but there are seven tokens (four "Grendel" and three "is" tokens).
Occurrences
There is a related distinction very closely connected with the type-token distinction. This distinction is the distinction between an object, or type of object, and an occurrence of it. In this sense, an occurrence is not necessarily a token. QuineWillard Van Orman Quine
Willard Van Orman Quine was an American philosopher and logician in the analytic tradition...
discovered this distinction, however only gave what he called an "artificial, but convenient and adequate definition" as "an occurrence of x in y is an initial segment of y ending in x."
If we consider for example the famous sentence: "A rose is a rose is a rose." We may equally correctly state that there are eight or three words in the sentence. There are, in fact, three word types in the sentence: "rose", "is" and "a." However, although there are eight word tokens in a token copy of the line, there aren't any tokens at all in the line itself. The line itself is a type. There are not eight word types in the line. It contains (as stated) only the three word types, ‘a,’ ‘is’ and ‘rose,’ each of which is unique. So what do we call what there are eight of? They are occurrences of words. There are three occurrences of the word type ‘a,’ two of ‘is’ and three of ‘rose’.
The need to distinguish tokens of types from occurrences of types arises, not just in linguistics, but whenever types of things have other types of things occurring in them.
See also
- MetalogicMetalogicMetalogic is the study of the metatheory of logic. While logic is the study of the manner in which logical systems can be used to decide the correctness of arguments, metalogic studies the properties of the logical systems themselves...
- FormalismFormalismThe term formalism describes an emphasis on form over content or meaning in the arts, literature, or philosophy. A practitioner of formalism is called a formalist. A formalist, with respect to some discipline, holds that there is no transcendent meaning to that discipline other than the literal...
- Is-aIs-aIn knowledge representation, object-oriented programming and design, is-a or is_a or is a is a relationship where one class D is a subclass of another class B ....
- Class (philosophy)Class (philosophy)Philosophers sometimes distinguish classes from types and kinds. We can talk about the class of human beings, just as we can talk about the type , human being, or humanity...
- Type theoryType theoryIn mathematics, logic and computer science, type theory is any of several formal systems that can serve as alternatives to naive set theory, or the study of such formalisms in general...
- Type physicalismType physicalismType physicalism is a physicalist theory, in philosophy of mind. It asserts that mental events can be grouped into types, and can then be correlated with types of physical events in the brain...
External links
- The Stanford Encyclopedia of Philosophy: "Types and Tokens" by Linda Wetzel.