Logic, passion and the problem of convergence

Our estimate of the likelihood of convergence on human-style intelligence depends on how we understand our various mental capacities. Here I revive David Hume's theory of motivation and action to argue that the most common understanding of the two conventionally recognized components of intelligence-reason and emotion-is confused. We say things like, 'Reason can overcome emotion', but to make this statement meaningful, we are forced to treat reason as a compound notion, as a forced and unhappy mixture of concepts that are incommensurate. An alternative is to parse intelligence in a different way, into two sets of capacities: (i) non-affective capacities, including logic, calculation and problem-solving; (ii) affective capacities, including wants, preferences and cares, along with the emotions. Thus, the question of convergence becomes two questions, one having to do with affective and one with non-affective capacities. What is the likelihood of convergence of these in non-human lineages, in other ecologies, on other worlds? Given certain assumptions, convergence of the non-affective capacities in thinking species seems likely, I argue, while convergence of the affective capacities seems much less likely.