Class (philosophy)
Encyclopedia
Philosophers sometimes distinguish classes from types and kinds
Natural kind
In philosophy, a natural kind is a "natural" grouping, not an artificial one. Or, it is something that a set of things has in common which distinguishes it from other things as a real set rather than as a group of things arbitrarily lumped together by a person or group of people.If any natural...

. We can talk about the class of human beings, just as we can talk about the type (or natural kind), human being, or humanity. How, then, might classes differ from types? One might well think they are not actually different categories of being
Category of being
In metaphysics , the different kinds or ways of being are called categories of being or simply categories. To investigate the categories of being is to determine the most fundamental and the broadest classes of entities...

, but typically, while both are treated as abstract object
Abstract object
An abstract object is an object which does not exist at any particular time or place, but rather exists as a type of thing . In philosophy, an important distinction is whether an object is considered abstract or concrete. Abstract objects are sometimes called abstracta An abstract object is an...

s, classes are not usually treated as universals
Universal (metaphysics)
In metaphysics, a universal is what particular things have in common, namely characteristics or qualities. In other words, universals are repeatable or recurrent entities that can be instantiated or exemplified by many particular things. For example, suppose there are two chairs in a room, each of...

, whereas types usually are. Whether natural kinds ought to be considered universals is vexed; see natural kind
Natural kind
In philosophy, a natural kind is a "natural" grouping, not an artificial one. Or, it is something that a set of things has in common which distinguishes it from other things as a real set rather than as a group of things arbitrarily lumped together by a person or group of people.If any natural...

.

There is, in any case, a difference in how we talk about types and kinds versus how we talk about classes. We say that Socrates
Socrates
Socrates was a classical Greek Athenian philosopher. Credited as one of the founders of Western philosophy, he is an enigmatic figure known chiefly through the accounts of later classical writers, especially the writings of his students Plato and Xenophon, and the plays of his contemporary ...

 is a token
Type-token distinction
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...

of a type, or an instance of the natural kind, human being. But notice that we say instead that Socrates is a member of the class of human beings. We would not say that Socrates is a "member" of the type or kind, human beings. Nor would we say he is a type (or kind) of a class. He is a token (instance) of the type (kind). So the linguistic difference is: types (or kinds) have tokens (or instances); classes, on the other hand, have members.

There is similarity between the concept of a class, and that of a set defined by its members. Here the class is extensional. If, however, a set is defined intensionally, then it is a set of things that meet some requirement to be a member. Thus such a set can be seen as creating a type. Note that it also creates a class from the extension of the intensional set. A type always has a similar class (though that class might have no members), but a class does not always have a corresponding type.

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