How do the sciences and their theories hang together?
The rise and continuing success of the sciences has overshadowed all of Western philosophy for the past 400 years. A central philosophical question about the sciences concerns how they are connected to one another. Within academic philosophy and in more popular discussions, talk about philosophical models of cross-scientific relations traditionally has been cast in the language of scientific “reduction.” I have contributed to a considerable critical literature on classical reductionism, and I have advanced and developed a larger conception of cross-scientific relations in terms of explanatory pluralism in science.
Explanatory pluralism enlists two important insights from the literature of the philosophy of science. The first is William Wimsatt’s distinction between intertheoretic relationships that arise from intralevel (successional) contexts as opposed to those that arise from interlevel (cross-scientific) contexts. Successional relations concern theoretical change over time within some particular science. Slow, gradual changes result in scientific evolution, whereas rapid, abrupt changes result in scientific revolutions. Cross-scientific relations, by contrast, concern comparisons at some particular moment in time of theories that have a common object of study (e.g., human behavior) but that arise from different sciences (e.g., social psychology and social neuroscience).
The second insight that explanatory pluralism enlists is Paul Churchland’s suggestion that the relative commensurability of two theories in science may fall anywhere on a continuum of possibilities from high to low. Sometimes two theories are thoroughly discontinuous with one another and their comparison falls at one end of this continuum. (Churchland has argued that this is the case with respect to the relationship between intentional psychologies and computational neuroscience.) In other cases, two theories are sometimes completely continuous and their comparison falls at the opposite end of the continuum. Such cases approximate the circumstances on which the classical reductionists focused. Statistical mechanics, for example, readily redescribes and captures the generalizations of classical thermodynamics. Comparisons of different pairs of scientific theories fall at various points on this continuum of commensurability between these two extremes.
Combining these insights, explanatory pluralism suggests that the models of the classical reductionists and of the New Wave reductionists confuse a variety of decidedly different sorts of intertheoretic relationships in science and, consequently, in at least some cases, mischaracterize their implications.
Explanatory pluralism envisions 4 different forms of scientific progress that can arise from exploring the relationships between theories in science. In successional contexts within a particular science over time, slow, gradual change—(1) scientific evolution—should be distinguished from rapid, abrupt change—(2) scientific revolution. The elimination of theories and the things they are committed to can arise in successional contexts, but that process is, famously, far more sudden and dramatic in the revolutionary cases. Crucially, these successional contexts should not be confused with cross-scientific settings, which examine the relationships between theories in different sciences at the same time. In cross-scientific settings, high intertheoretic commensurability results in something that approaches (3) classical reduction, vindicating the relevant theory of the upper-level science. Low intertheoretic commensurability in cross-scientific contexts, by contrast, reveals divergent theoretical proposals, which, ironically, can occasion both insular declarations about the autonomy of disciplines and the process of (4) theoretical co-evolution, simultaneously.