The Incommensurability Thesis and the Status of Knowledge

The view that inquiry can be understood in terms of rhetorical theory can be traced to Thomas Kuhn's influential work, The Structure of Scientific Revolutions (1962). Kuhn is often cited by scholars concerned with the discursive strategies by which the natural and social or human sciences justify themselves and their specific claims. Kuhn's legacy is well captured by Nelson, Megill, and McCloskey in the opening essay of The Rhetoric of the Human Sciences (1987) where they link him to Stephen Toulmin and Chaïm Perelman as instigators of the study of the Rhetoric of Inquiry. In their words, Kuhn's landmark classic "challenges philosophy to account for the actual operation of scientific communities—their professional devices of communication and socialization, their political structures, their reliance on aesthetics, and their rhetorical dependence on persuasion" (Nelson, Megill, and McCloskey 1987, 12). Despite this reaction, however, Kuhn's project was in many ways modest. He was not seeking to develop a sociology of science or a rhetoric of inquiry. He sought only to account for the form of modern science's history, which is not marked by linear progress, but by a succession of dominant frameworks, or what he termed paradigms.

As I will argue in this essay, Kuhn's conception of paradigms is incompatible with rhetoric, except during scientific revolutions or under conditions of incommensurability. Incommensurability is a problematic category, however, for the opening it affords rhetoric ultimately undermines the very idea of paradigms. Consequently, locating rhetoric within normal science either undermines the very category distinctions that provide science with its specificity, or reduces rhetoric from a particular genre of discourse directed toward human agency to "rhetoricality," an aspect of all discourse. As we shall see, such blurring of genre distinctions is itself fundamentally problematic, for science and rhetoric as discursive genres and practices are themselves incommensurable, even if not in Kuhn's terms.

Rhetoric and revolution

Kuhn observed that modern science is characterized by the bracketing of major disagreements regarding basic assumptions except during periods of "crisis." While pre-modern inquiry saw the contemporaneous co-existence of fundamentally incompatible frameworks, each competing for adherents, modern science normally excludes such divisions. Instead, modern science is characterized by a succession of frameworks. Only at periods of transition that are temporally bounded, for which Kuhn coined the term "scientific revolutions," does more than one framework have currency within a given sub-specialty (1962, 10-22).

Kuhn accounts for this curious historical phenomenon by arguing that modern science is precisely constituted through an enforced bracketing of debates over first principles. The first principles, or paradigm, of any field are more than a set of epistemological or ontological assumptions. They are the set of rules constitutive of science as an activity. They orient scientists in their work, providing background assumptions, methodological principles, criteria of validity, a research agenda, and so on. The hegemony of a paradigm frees scientists from having to justify their work philosophically, socially, or politically. As Kuhn observes, normally science has the form of puzzle solving (35-42). He even likens it to a game, and like any game the participants need not concern themselves with the extrinsic validity of its rules or of the game itself. As Kuhn notes:

Though many scientists talk easily and well about particular individual hypotheses that underlie a concrete piece of current research, they are little better than laymen at characterizing the established bases of their field, its legitimate problems and methods. If they have learned such abstractions at all, they show it mainly through their ability to do research. That ability can, however, be understood without recourse to hypothetical rules of the game. (47)

Paradigms render modern science possible by producing practitioners and practices rather than by providing explicit knowledge of the principles such practices instantiate. In Foucault's language, we could say that practices are discursive formations (see Foucault 1972, 31-39). They are productive: they give to knowledge...