Abstract

Semantic essentialism holds that any scientific term that appears in a well-confirmed scientific theory has a fixed kernel of meaning. Semantic essentialism cannot make sense of the strategies scientists use to argue for their views. Newton's central optical expression "light ray" suggests a context-sensitive view of scientific language. On different occasions, Newton's expression could refer to different things depending on his particular argumentative goals - a visible beam, an irreducibly smallest section of propagating light, or a traveling particle of light. Essentialist views are too crude to account for the richness and subtleties present in actual episodes of scientific debate and theory-change.