Constructivist theory has its roots in a number of disciplines, including philosophy, anthropology, the natural sciences, semiotics, socio-linguistics, and education. Its lineage has been variously described (see, for example, Duffy and Cunningham, 1996; and Entwistle, Entwistle, and Tait, 1991). In the field of education, both Rousseau and Dewey are often cited as incorporating constructivist perspectives into their views of teaching and learning. More recently, the focus on constructivism has emerged from the push for reforms in specific content areas, with science and mathematics education at the forefront (Brooks and Brooks, 1993).

In education, constructivism is often discussed as a philosophy or instructional approach. As Catherine Fosnot observes, however, "Constructivism is not a theory about teaching. It's a theory about knowledge and learning" (Brooks and Brooks, 1993, p. vii). The confusion of the two has led both to controversy and to a tendency to consider constructivism as merely one in a broad array of concepts on which teachers can draw in seeking to improve student learning. For any learning theory to be of use, it is certainly necessary to identify and explore its implications for teaching. But it is critically important to consider constructivism first purely through the lens of learning theory, i.e., what is (according to the constructivist perspective), rather than what should be.

Duffy and Cunningham (1996) point out that "the term constructivism has come to serve as an umbrella term for a wide diversity of views" (p. 171). Some authors distinguish between cognitive constructivism, which focuses on the individual learner, and social constructivism, which emphasizes learning as occurring within the context of dialogue and social interaction (Duffy and Cunningham, 1996).

Definitions of constructivism under any of these views, however, include as central the idea that knowledge is "constructed" by the learner. For example, Honebein, Duffy, and Fishman (1991) state, "Basically, constructivism proposes that knowledge or meaning is not fixed . . . but rather is constructed by individuals through their experience . . . in a particular context" (p. 88). Embedded in this statement are a number of concepts that run counter to the beliefs still shaping instruction in U.S. schools today: that learning is adaptive, a process of building functional understandings rather than of uncovering fixed truths; that learning is an active process controlled by the learner; and that learning and the context for learning are deeply intertwined (Brooks and Brooks, 1993; Duit, 1995; Duffy and Cunningham, 1996). There are other important concepts as well, particularly the role of social interaction in both mediating and facilitating the learning process.

Learning as an adaptive activity. Constructivist theory characterizes learning as sense-making. Brooks and Brooks (1993), for example, state, "Each of us makes sense of our world by synthesizing new experiences into what we have previously come to understand" (p. 4). Learning is a process of developing ever-more-powerful understandings; the activity is not one of acquiring a fixed body of knowledge, but of building concepts and explanations that allow us to function effectively in a given context and that adequately account for the circumstances presented to us.

Taken as the advancement of understanding, the cognitive endeavor starts from what happens to be currently adopted and proceeds to integrate and organize, weed out and supplement, not in order to arrive at truth about something already made but in order to make something right--to construct something that works cognitively, that fits together and handles new cases, that may implement further inquiry and invention. (Bauersfeld, 1995, p. 144, quoting Goodman and Elgin, 1988)

Knowledge, in this view, is not fixed; it is not possible, in fact, to determine objective truth with any absolute certainty. Duffy and Cunningham (1996) state that "what we choose to call knowledge is a consensus of beliefs, a consensus open to continual negotiation" (p. 178). Rather than the approximation of objective reality, then, "viability" is the appropriate measure of understanding. As von Glasersfeld (1995a) observes, "To the biologist, a living organism is viable as long as it manages to survive in its environment. To the constructivist, concepts, models, theories, and so on are viable if they prove adequate in the contexts in which they were created" (pp. 7-8).