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Quantum physics poses a serious challenge to the intuition. An electron, for example, can act both as a wave and as a particle. This curious aspect of nature has been known to physicists since the early part of the 20th century, yet it still seems very weird, even to those schooled in quantum mechanics. Here a historian of science argues that wave-particle duality can be seen a consequence of the fact that like particles are identical to one another, a property he terms "identicality."