Quantum Mechanics as a Principle Theory

In an article written for the London Times in 1919, Einstein presented a remarkably clear and succinct, non-technical account of the theory of relativity. He began by drawing a distinction between &constructive' and &principle' theories, and pointed out that the theory of relativity should be understood as a principle theory &in order to properly grasp its nature'. (I use the translation in Einstein (1954), which is di!erent from the original translation in the Times. See Einstein (1954, p. 228).) Here I apply Einstein's distinction to the problem of interpreting quantum mechanics. I show how quantum mechanics, too, can be understood as a principle theory, and I examine some puzzling features of &entangled states' from this perspective.