  Reid identifies three particularly important senses in which the strength of a motive can be measured: by, to use his terms, its ‘prevalence’, its ‘animal strength’, or its ‘rational strength’. According to the view that associates strength with prevalence, the strongest motive is just the motive on which the agent acts. Under this view, there is no way of assessing the strength of motives prior to seeing what the agent does. The animal strength of a motive is the degree to which it is felt, the degree to which the agent might be said to have an urge for its object. The rational strength of a motive is the degree to which the act it dictates is judged to be worthwhile by the agent. 