Even natural-kind concepts shift as empirical knowledge of the object changes.

Evidence

In contrast, this volumes argues that a concept involves a theoretical and empirical analysis of the object or phenomenon referred to by the word. A good concept draws distinctions that are important in the behavior of the object. The central attributes that a definition refers to are those that prove relevant for hypotheses, explanations, and causal mechanisms. In a theoretical and empirical view of scientific concepts their semantics change as our understanding of the phenomenon changes. Take the example of “copper”: the very definition or concept of copper has changed, reflecting new knowledge generated by chemists. — Gary Goertz, Social Science Concepts, 72

Categorization

• XREF: Chimes with the reader’s archive on scientific progress and paradigm shift; a copper concept is a clean, miniature case of theory-laden observation.
• SEED: Angle: ‘Your definitions are hypotheses in disguise’ — why the best analysts refuse to fix terminology before they understand the phenomenon.