processes of conceptual or theory change. In this view, at critical junctures, as evidence anomalies build up against the established theory, there can occur wholesale restructurings of the theoretical landscape—a paradigm shift, according to Kuhn (1962). For example, in both Kuhn’s account of scientific revolutions and Chi’s (1992) and Carey’s (1988, 1991) accounts of critical points of conceptual restructuring in cognitive development, not only do new concepts enter a domain, but also existing concepts change their meaning in fundamental ways because the theoretical structure within which they are situated radically changes (e.g., changes in concepts like force, weight, matter, combustion, heat, or life). Nersessian (1989) provides a good example of the semantic changes that occur when motion and force are examined across Aristotelian, Galilean, and Newtonian frameworks.
The view of science as practice is emphasized by anthropologists, ethnographers, social psychologists, and the cognitive and developmental psychologists who study “situated cognition” (Brown, Collins, and Duguid, 1989; Lave and Wenger, 1991; Latour, 1990, 1999; Rogoff and Lave, 1984). This view focuses on the nature of scientific activity, both in the short term (e.g., studies of activity in a particular laboratory or a program of study) and historically (e.g., studies of laboratory notebooks, published texts, eyewitness accounts). Science as practice suggests that theory development and reasoning are components of a larger ensemble of activity that includes networks of participants and institutions (Latour, 1999; Longino, 2002); specialized ways of talking and writing (Bazerman, 1988); modeling, using either mechanical and mathematical models or computer-based simulations (Nersessian, 2005); and development of representations that render phenomena accessible, visualizable, and transportable (Gooding, 1989; Latour, 1990; Lehrer and Schauble, 2006).
This perspective serves as a useful foil to the tendency of “pure” cognitive approaches to science to minimize the fact that individual scientists or groups of scientists are always part of a wider social environment, inside and outside science, with which they are in constant communication and which has strongly shaped their knowledge, skills, resources, motives, and attitudes. This interaction between social and cognitive factors is well illustrated in Thagard’s (1998a, 1998b) account of the pioneering research by Barry Marshall and Robin Warren. They received the Nobel prize in medicine in 2005 for their discovery of the bacterial origins of stomach ulcers. Until 1983, the prevailing view was that gastric ulcers were caused by lifestyle and stress. When Marshall and Warren suggested that ulcers were caused by the bacterium Helicobacter pylori, their claim was viewed as preposterous