In 1927, Werner Heisenberg used the idea of wave function reduction to explain quantum measurement.[5] Nevertheless, it was debated, for if collapse were a fundamental physical phenomenon, rather than just the epiphenomenon of some other process, it would mean nature was fundamentally stochastic, i.e. nondeterministic, an undesirable property for a theory.[2][6] This issue remained until quantum decoherence entered mainstream opinion after its reformulation in the 1980s.[2][4][7] Decoherence explains the perception of wave function collapse in terms of interacting large- and small-scale quantum systems, and is commonly taught at post-introductory level (e.g. the Cohen-Tannoudji textbook).[8] The quantum filtering approach[9][10][11] and the introduction of quantum causality non-demolition principle[12] allows for a classical-environment derivation of wave function collapse from the stochastic Schrödinger equation.