Epistemology is the branch of philosophy concerned with the theory of knowledge. Epistemology studies the nature of knowledge, justification, and the rationality of belief.

Ernst von Glasersfeld defines radical constructivism by the following two basic principles:

1) Knowledge is not passively received either through the senses or by way of communication, but is actively built up by the cognising subject.

2) The function of cognition is adaptive and serves the subject's organization of the experiential world, not the discovery of an objective ontological reality.

(http://pespmc1.vub.ac.be/CONSTRUC.html)

According to this philosophy, knowledge is not a passive mapping of outside objects, but an active construction by the subject. That construction is not supposed to reflect an objective reality, but to help the subject adapt or “fit in” to the world which it subjectively experiences.

This means that the subject will try to build models which are coherent with the models which it already possesses, or which it receives through the senses or through communication with others. Since models are only compared with other models, the lack of access to exterior reality no longer constitutes an obstacle to further development. In such an epistemology, knowledge is not justified or “true” because of its correspondence with an outside reality, but because of its coherence with other pieces of knowledge…

Model construction can be seen as a trial-and-error process, where different variations are generated, but only those variations are retained which “fit in” with the rest of the experiential material [See Vicarious Selectors]. Thus, the process is selectionist (Cziko, 1995; Bickhard & Ter Veen, 1995) rather than instructionist: instead of instructing the subject on how to build a model, the (inside or outside) environment merely helps it to select the most “fit” models among all of the subject's autonomously generated trials.

Many constructivists tend to emphasize the role of social interaction in this selection process: those models will be retained about which there is a consensus within the community. This is the social constructivist position which is popular especially in the social sciences and humanities. Psychologists ... on the other hand, emphasize the individual subject, who tries to find coherence between his or her different models and perceptions. The selectionists ... emphasize the role of the outside environment in weeding out inadequate models. For obvious reasons, this more “realist” position is most popular in the natural sciences. My own philosophy is pragmatic, and acknowledges the combined role of individual, social and physical (“objective”) factors in the selection of knowledge (Heylighen, 1993, 1997).

Although constructivists usually also accept some form of a coherence view of truth, few people have proposed concrete mechanisms that show how the dynamic process of construction (variation) can result in the static requirement of coherence (selective retention). The originality of Pask's Conversation Theory is that it provides a detailed formal model of such mechanisms. The metaphor of conversation is aptly chosen to describe such a process of cognitive interaction, in which concepts are exchanged, combined and recombined (the construction phase), with the aim of achieving agreement about shared meanings (the coherence phase). Although the conversation metaphor seems to favor the social construction of knowledge, Pask is quick to point out that his theory applies equally well to interactions between different roles or perspectives (“p-individuals”) within a single individual. I have suggested elsewhere (Heylighen, 1990c) that the conversational perspective could even be extended to interactions between observers and objects.

http://pespmc1.vub.ac.be/Papers/Pask-Bootstrapping.pdf

Contrast with Correspondence Epistemology.