Levels of Explanation

One of the most obvious facts about contemporary science is that it is partitioned into different disciplines. Physicists, biologists, psychologists, and economists each have a distinctive vocabulary in which they formulate laws and explain the events which interest them. In the heyday of positivism, philosophers tried to provide these scientists with a translation manual-a manual which would enable the physicist to restate in his own terms what the economist was saying when he offered an economic explanation for an increase in unemployment.1 But such a manual could not be produced and philosophers of science were forced to acknowledge a plurality of scientific theories. If we have more than one science on our hands, then we must provide some account of the relationship between them. An important part of this task is to effect a reconciliation between two widely shared opinions. On the one hand, there is the conviction that physics is the fundamental science. On the other hand, there is the insistence that special sciences such as biology, psychology, and economics are autonomous disciplines whose lawlike statements and explanatory claims stand in no need of support from physics. Given these conflicting pressures, the levels metaphor naturally suggests itself as a way of visualizing the structure of science. According to this picture, there is a hierarchy made up of different levels of explanation. Physics is at the base of this hierarchy and the rest of the structure depends upon it. But the higher reaches of the scientific edifice have explanatory features which could not be discerned by someone who confined himself to exploring the ground floor. Of course, this metaphor is crucially vague until we say how exactly these higher level features can depend on those of the foundations when there are explanations which cannot be discovered at the base. In the first section of the paper, I try to formulate the claim that physics is the fundamental science. My formulation gives physics a certain ontological and causal primacy but it does not grant any special status to physical explanations. The second section describes two popular accounts of the relationship between the different sciences, both of which hold that non-physical explanations are underwritten by physical explanations. In the third section, I urge that these models are acceptable only if we can