Introduced by Niels Bohr, this principle deals with the wave/particle duality of matter in general and sub-atomic matter in specific.

The principle says that in order to fully describe an occurence, it is neccessary to know even mutually exclusive characteristica. This is not always possible according to Heisenberg Uncertainty Principle, but serves as a philosphical way to view what seems to be paradoxes on the sub-atomic scale.