In philosophy, the terms type and token are sometimes used to describe formal objects and instances of those objects. A type is a category or class of an object or event, whereas a token is a specific instance or occurance of a type of object or event.
Types and tokens may be most clearly demonstrated using words. Consider the following:
space, time, space, time, time, time.
The question may be asked, how many words are in that line? The answer will either be six, if one is referring to individual words, or tokens, or two, if one is referring to types of words.
Specifically, there are two types of words in that sentence, “space” and “time”, but there are six tokens, six individual occurances of those types. There are two tokens of the type “space” and four tokens of the type “time”.
The terms type and token are used in various areas of philosophy.
In philosophy of mind, for instance, the terms are used to describe versions of identity theory, which states that mental states are actually, or are identical to, brain states. Type identity theory refers to specific types of brain states always producing the same type of mental state, while token identity theory would say that the brain and mental states are still identical, but not in a way that can be directly typed. One type of brain state may produce different types of mental states from token to token.