 Those who are less inclined towards behaviourism might, however, not find this lack of uniqueness in Bolker’s theorem to be a problem. James Joyce (1999), for instance, thinks that Jeffrey’s theory gets things exactly right in this regard, since one should not expect that reasonable conditions imposed on a person’s preferences would suffice to determine a unique probability function representing the person’s beliefs. It is only by imposing overly strong conditions, as Savage does, that we can achieve this. However, if uniqueness is what we are after, then we can, as Joyce points out, supplement the Bolker-Jeffrey axioms with certain conditions on the agent’s comparative belief relation (e.g. those proposed by Villegas 1964) that, together with the Bolker-Jeffrey axioms, ensure that the agent’s preferences can be represented by a unique probability function and a desirability function that is unique up to a positive linear transformation.