  Philosophical theories of reduction would have it that, say, quantum mechanics reduces classical mechanics through the derivation of the laws of classical physics from those of quantum physics. Most physicists would, on the other hand, speak of quantum mechanics reducing to classical mechanics in some kind of correspondence limit (e.g., the limit as Planck’s constant \((h/2\pi)\) goes to zero). Thus, the second type of intertheoretic reduction noted by Nickles fits the following schema: