Constructivism is an epistemological stance regarding the nature of human knowledge, having roots in the writings of Epicurus, Lucretious, Vico, Berkeley, Hume, and Kant. Modern constructivism also contains traces of pragmatism (Peirce, Baldwin, and Dewey). In mathematics education the greatest influences are due to Piaget, Vygotsky, and von Glasersfeld. See Confrey and Kazak (2006) and Steffe and Kieren (1994) for related historical accounts of constructivism in mathematics education.
There are two principle schools of thought within constructivism: radical constructivism (some people say individual or psychological), and social constructivism. Within each there is also a range of positions. While radical and social constructivism will be discussed in a later section, it should be noted that both schools are grounded in a strong Skeptical stance regarding reality and truth: Knowledge cannot be thought of as a copy of an external reality, and claims of truth cannot be grounded in claims about reality.