Abstract
An old result of Brittin to the effect that dissipative systems belonging to a certain class lend themselves to canonical quantization in the Heisenberg picture but not in the Schrödinger picture is shown to be incorrect. It is shown that canonical quantization is impossible in the presence of nonconservative forces, no matter which of the two pictures one chooses. This restores the equivalence of the Heisenberg and Schrödinger pictures.

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