This contribution argues that Bohr's notion of complementarity can be traced back to the Laozi which he would have read. In Chinese philosophy, polar contrasts such as yin and yang are not regarded as mutually exclusive; they are co-present, existing as a harmonious Whole. Such a conception of metaphysics and logic stood Bohr in good stead for characterising quantum phenomena which are at once both wave and particle. His notion of complementarity bears witness to the possibility of communication and understanding between two different philosophical approaches and scientific traditions—this account adds to Lloyd's concept of semantic stretch.
Abstract Bohr took it as the key fact of QT that neither of the models for describing the behaviour of systems offered by classical physics— neither the ‘particle picture’ nor the ‘wave picture’—fitted q-systems in all aspects of their behaviour. More particularly he took these two pictures to be ‘complementary’—when one fitted the other one did not. This failure of fit was seen by Bohr as usually only partial however, as a degree of’imprecision of fit’ rather than a total failure of fit; and it is in terms of this notion that Bohr was then able to give expression to his principle of complementarity, viz. that the degrees of imprecision of fit of the wave and particle pictures are reciprocally related: to the extent that one of the pictures fits well, the other fits badly. In this chapter I shall discuss these notions in the context of a more general discussion of Bohr’s philosophy of Quantum Theory.