Bohr’s principle of complementarity – the heart of the Copenhagen philosophy – implies that quantum phenomena can only be described by pairs of partial, mutually exclusive, or ‘complementary’ perspectives. Though simultaneously inapplicable, both perspectives are necessary for the exhaustive description of phenomena. Bohr aspired to generalize complementarity into all fields of knowledge, maintaining that new epistemological insights are obtained by adjoining contrary, seemingly incompatible, viewpoints. [...] The value of Bohr’s philosophy for the advancement of physics is controversial. His followers consider complementarity a profound insight into the nature of the quantum realm. Others consider complementarity an illuminating but superfluous addendum to quantum theory. More severe is the opinion that Bohr’s philosophy is an obscure ‘web of words’ and mute on crucial foundational issues.
Mara Beller, "Bohr, Niels (1885-1962)", Routledge Encyclopedia of Philosophy