A term coined by Danish physicist Neils Bohr applying to the two mutually exclusive ways of describing light (as a wave and (not “or”) as a particle). Consciousness, as well, seems to be describable under two mutually exclusive accounts: either through a 3rd person account (e.g. pain is a property caused by tissue damage and in turn causes words such as “ouch”) or a 1st person account (pain feels like this: [insert sensation]).
Some philosophers have abandoned attempts to reduce 3rd person accounts to 1st person or 1st person accounts to 3rd person. Instead, they invoke Bohr’s complementarity thesis as a metaphor to explain these mutually exclusive descriptions. Neither 1st or 3rd person accounts has an explanatory monopoly over the other, they argue. Both are true of consciousness.