I Downward Causation and the Metaphysics of Causation
Three Grades of Downward Causation
Francesco Orilia and Michele Paolini Paoletti
Following a traditional and intuitively appealing picture, assume a layered model of reality: there are different ontological levels, with different entities—objects, properties, relations, events—belonging to the different levels. These levels are more or less identifiable with the domains of the special sciences, the micro- and macro-physical levels with the lowest position in the hierarchy, and then the chemical, the biological, the psychological, the sociological, with increasingly higher positions. The lower levels ground the higher ones and thus what happens at a higher level is somehow governed or constrained by, dependent on, what goes on at the lower founding level. Once we have this picture, we can dress it with downward causation: causes belonging to a certain higher level have effects at a lower level. Setting aside some important details, emergentism can be roughly characterized as a doctrine that associates downward causation with the layered model. Not a bad idea, one may say, for this further element is palatable and plausible: we seem to have prima facie evidence that there is such a thing.
For example, a cell directs and controls certain activities performed by its constituents, thus causing something involving them. Another example: when our friend John decides or wills1 to raise his arm, he seemingly causes something at a lower level, i.e., at the level of his neurons: he causes or directs the activities of his neurons, so as to achieve the desired result of the volition, i.e., raising his arm.
But can there be downward causation? As is well known, Kim has questioned that there can be such a thing, roughly on the ground that it is incompatible with upward determination, as Kim (1999) calls it, i.e., the fact that the lower levels ground the higher ones. More specifically, he has questioned mental downward causation, i.e., causation going from the psychological level to a lower level, which we shall call, for simplicity’s sake and in a general fashion, a physical level (although we may want to think of it as a biological level or even, more precisely, a neurophysiological level). Here we shall focus on this. We shall briefly review in the next two sections the context in which Kim operated and how he attacked downward mental causation. We shall then move on to consider three possible ways or models in which, with increasing strength, we can find room for it in the layered model—room, we may say, for some form of psychological emergentism. As we shall see, the difference in grade of downward causation in the three models is related to a difference in the manner in which causal relata are conceived of.