Although mind-brain identity remains controversial, many other identities of ordinary things with scientific ones are well established. For example, air is a mixture of gases, water is H[subscript 2]O, and fire is rapid oxidation. This paper examines the history of 15 important identifications: air, blood, cloud, earth, electricity, fire, gold, heat, light, lightning, magnetism, salt, star, thunder, and water. This examination yields surprising conclusions about the nature of justification, explanation, and conceptual change.