We provide a novel perspective on "regularity" as a property of representations of the Weyl algebra. We first critique a
proposal by Halvorson [2004, "Complementarity of representations in quantum mechanics", Studies in History and
Philosophy of Modern Physics 35(1), pp. 45--56], who argues that the non-regular "position" and "momentum" representations of the Weyl algebra demonstrate that a quantum mechanical particle can have definite values for position or momentum, contrary to a widespread view. We how that there are obstacles to such an intepretation of non-regular representations. In Part II, we propose a justification for focusing on regular representations, pace Halvorson, by drawing on algebraic methods
