Abstract
The author recalls the problem of choosing an ordering for the terms in a Hamiltonian of the form H(p, q) of finite dimension in p, q. He demonstrates that most orderings which provide one with a Hermitian operator are in fact redundant and he gives a general form for ordering rules in terms of arbitrary parameters. He concludes that differences in the choice of an ordering contribute differences to the physics which are only of order 2 and higher. He provides an example of a Hamiltonian for which the spectrum is explicitly dependent on the choice of quantisation rule (operator ordering). He compares the method of characterising operator ordering rules with that of Cohen (1966, 1970). Finally he generalises Cohen's method to the case of all linear quantisation rules and shows how his rule is a special case.