Type-token relations

The type–token distinction is used in disciplines such as logic, linguistics, metalogic, typography, and computer programming to clarify what words mean.

The sentence "they drive the same car" is ambiguous. Do they drive the same type of car (the same model) or the same instance of a car type (a single vehicle)? Clarity requires us to distinguish words that represent abstract types from words that represent objects that embody or exemplify types. The type–token distinction separates types (representing abstract descriptive concepts) from tokens (representing objects that instantiate concepts).

For example: "bicycle" is a type that represents the concept of a bicycle; whereas "my bicycle" is a token that represents an object that instantiates that type. In the sentence "the bicycle is becoming more popular" the word "bicycle" is a type representing a concept; whereas in the sentence "the bicycle is in the garage" the word "bicycle" is a token representing a particular object.

(The distinction in computer programming between classes and objects is related, though in this context, "class" sometimes refers to a set of objects (with class-level attribute or operations) rather than a description of an object in the set.)

The words type, concept, property, quality, feature and attribute (all used in describing things) tend to be used with different verbs. E.g. Suppose a rose bush is defined as a plant that is "thorny", "flowering" and "bushy". You might say a rose bush instantiates these three types, or embodies these three concepts, or exhibits these three properties, or possesses these three qualities, features or attributes.

Property types (e.g "height in metres" or "thorny") are often understood ontologically as concepts. Property instances (e.g. height = 1.74) are sometimes understood as measured values, and sometimes understood as sensations or observations of reality.

Some say types exist in descriptions of objects, but not as tangible physical objects. They say one can show someone a particular bicycle, but cannot show someone the type "bicycle", as in "the bicycle is popular.". However types do exist in the sense that they appear in mental and documented models.

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