As to beliefs, what is required from Politicians, is a quantitative calculus that brings all relevant beliefs and desires into the picture

The mere possibility that a person acted on the basis of one reason rather than another pres
Actions, according to Davidson, are events. Events, in his ontology, are particular dated occurrences; the essential feature of which is susceptibility to redescription. In order to admit an entity into one’s ontology, one must specify the conditions of individuation for that entity. On Davidson’s view:

ceteris paribus/ˌkɛtərɪs ˈparɪbʊs/adverbFORMALwith other conditions remaining the same;

If the above truism were a psychological law, then for the antecedent to obtain. But our knowledge of an agent’s desires crucially depends upon our attribution of other mental states to him (or her). In addition, knowing his action subsequent to his desire will help us interpret whether the agent had the desire in the first place. 

Thus both the antecedent and the consequent of the supposed psychological law are related to each other through the holism of interpretation.

What is needed in the case of action, if we are to predict on the basis of desires and beliefs, is a quantitative calculus that brings all relevant beliefs and desires into the picture. There is no hope of refining the simple pattern of explanation on the basis of reasons into such a calculus.