naturalkind

Natural kind is a term used in the philosophy of science to describe a category of things in the natural world that is thought to reflect real, discoverable features of nature rather than arbitrary human classifications. Natural-kind terms in science are typically taken to name kinds that have stable causal powers or underlying essences that make their members behave similarly under normal conditions. Classic examples often cited include water, which is taken to be the substance H2O, gold as a chemical element with atomic number 79, and the biological kind tiger.

There are competing accounts of what makes a kind a natural kind. A historically influential view, associated with Saul Kripke and Hilary Putnam, holds that natural kinds have a rigid designation across possible worlds; the term refers to the actual kind in the world, grounded in an underlying essence or natural mechanism. An alternative approach, the homeostatic property cluster account, proposed by other philosophers, suggests that natural kinds are groups of properties that reliably tend to co-occur due to causal powers, even if no single essence fully defines the kind.

In practice, the natural-kind framework aims to explain why scientific classifications are often robust across varied contexts and how they support successful prediction and explanation. Critics argue that boundaries between kinds can be vague or context-sensitive, and that not all scientific categories track a single underlying essence. The debate continues to influence discussions in metaphysics, philosophy of science, and the interpretation of scientific classification.