 While Heisenberg is willing to admit the limited utility of the principle, he does not view it as a fundamental principle of quantum theory the way that Bohr does. Instead Heisenberg argues that “[i]t must be emphasized that this [correspondence] is a purely formal result; it does not follow from any of the physical principles of quantum theory” (Heisenberg 1930, p. 83). In other words, the correspondence is to be interpreted as a purely mathematical result, not as revealing any deep connection between the quantum and classical theories, and certainly not as a principle of quantum theory itself. For Heisenberg, quantum mechanics is a closed theory [Abgeschlossene Theorie], an axiomatic system complete in itself, not one that in any way depends on classical  mechanics.[11]