Kinds

Kinds is a general term for a class of entities that share common properties or a common function. In philosophy, the word is used to distinguish natural kinds from social kinds. Natural kinds are groupings that reflect intrinsic features of the world and tend to have explanatory power for a wide range of phenomena; examples often cited are water (H2O), gold, and the chemical element iron, or biological species such as the domestic cat. Social kinds are categories created by human conventions, norms, or social practices, such as money, marriage, or social roles, which may not correspond to stable natural features but nonetheless influence behavior and institutions.

Languages and philosophy of language distinguish kinds from tokens. A kind is the general class of objects under a term, while a token is a particular instance of that class. For example, the word "table" denotes the kind consisting of all objects that count as tables; each physical table is a token of that kind. The study of kinds also intersects theories of similarity, such as prototype theory, which suggests that categories are organized around central exemplars rather than strict definitions, and around family resemblance rather than necessary and sufficient conditions.

In science and everyday use, classifying into kinds helps prediction, explanation, and communication. However, boundaries between kinds can be fuzzy, and categories may evolve with new evidence or social change. Some debates focus on whether natural kinds exist as fixed, discoverable structures or are practical constructs for organizing knowledge.