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The complementarity principle, the way usually accepted was originally proposed by Niels Bohr. First, he postulated that one could perceive the quantum world only through classical measurements. But the classical measurements of a pair of physical quantities (or "observables") such as position and momentum could only be made in a mutually exclusive manner. Such a pair he called complementary. Thus he made the complementarity principle. He even extended this principle to a pair of concepts like the wave and particle pictures of light, which were confronted with each other in classical physics. Namely, if one is to detect light as a wave, he must abandon the possibility of detecting its particle nature, or vice versa. This sounds similar to the uncertainty principle of Werner Heisenberg, which says that two mutually conjugate observables cannot possibly be detected simultaneously beyond a certain level of inaccuracy. The product of uncertainties of the conjugate observables cannot be smaller than a certain universal constant called Planck's constant h. However, Bohr's principle is a wider and more vague concept. The wave and particle pictures of light are not such a conjugate pair, yet Bohr tried to establish that they were not possibly detected in a single experiment because of the complementarity principle. Was he right?