Constructivism is a perspective in philosophy that views all of our knowledge as "constructed", under the assumption that it does not necessarily reflect any external "transcendent" realities; it is contingent on convention, human perception, and social experience.
Constructivism criticizes essentialism, whether it is in the form of medieval realism, classical rationalism, or empiricism.
The expression "Constructivist epistemology" was first used by Jean Piaget, 1967, with plurial form in the famous article from the "Encyclopédie de la Pléiade" Logique et Connaissance scientifique (Logic and Scientific knowledge), an important text for epistemology. He refers directly to the mathematician Brouwer and his radical constructivism.
Moreover, in 1966, Peter L. Berger and Thomas Luckmann published The Social Construction of Reality, which has initiated social constructionism.

History
The common thread between all forms of constructivism is that they do not focus on an ontological reality, but instead on the constructed reality. Indeed, a basic presupposition of constructivism is that Reality-As-It-Is-In-Itself (Ontological Reality) is utterly incoherent as a concept, since there is no way to verify how one has finally reached a definitive notion of Reality. One must already have Reality in mind--that is, one must already know what Reality consists of--in order to confirm when one has at last "hit bottom". Richard Rorty has justly said, therefore, that all claims to Realism can be reduced to intuition (Consequences of Pragmatism, chs. 9, 11). At bottom, then, it seems that the Realist/Anti-Realist debate can be reduced to a conflict of intuitions: "It seems to us that..." "Well, it seems to us that...". A realist would not like to construe the argument in this way, and would say that someone is misled, that one of these groups seems correctly, and another group perceives incorrectly. Again, though, constructivists will complain that there is no way to confirm one way or another, since the goal of inquiry (Reality) must be assumed to be understood at the outset. The Realist hope, in a constructivist understanding, is simply an arbitrary freezing of the infinite regress of circularity that plagues human reasoning which vainly hopes to validate itself with a secure foundation.
Famously, this rather relativist theory is seen by some to contradict itself as a true affirmation: because this view also is "constructed," that is, made and not found, built by human hands rather than discovered in Nature or Reality. Consistent constructivists, however, will reply to this tu quoque (your theory, too!) critique with a rejoinder of their own: bien sur! (of course our theory, too!). It is an obvious and foolish claim for a constructivist to play a realist with regard to his or her own perspective. It is the basic claim of constructivism which allows one to reject altogether claims to universalism, realism, or objective truth. Consistent constructivists will not make any of these "hard" claims for their views, for they believe that their position is merely a view, a more or less coherent way of understanding things, that has thus far worked for them as a model of the world. This notion is deeply indebted to Darwinian theory, as it is claimed by constructivists that human understanding, as the product of Natural Selection, can be said to provide no more "true" understanding of the world as it is in itself than is absolutely necessary for human survival. Naturally, one will ask constructivists why they accept Darwin as a foundational thesis, if there are no "truer" explanations of the world than any other. Constructivists will reply that Darwinism epistemology undercuts itself as a transparent window onto the world, and reveals only its plausibility as an account. Insofar as someone desires a naturalistic account of the world that makes sense of a variety of data, Darwinism is the best (indeed, virtually only) explanatory schema that meets the requirements of modern scientific inquiry. Modern scientific inquiry, however, constructivists wish to point out, is itself subject to the contingencies of history, culture, language, and the tenuousness of the human intellect. For many, though, this self-reflexive anti-epistemology will not prove useful, desirable or very sturdy as an explanatory framework. An excellent account of the Self-Refutation Charge is given in Barbara Herrnstein Smith's Belief & Resistance, chapter 5 (pp. 73-87; "Unloading the Self-Refutation Charge").
Constructivism proposes new definitions for knowledge and truth that forms a new paradigm, based on inter-subjectivity instead of the classical objectivity and viability instead of truth. The constructivist point of view is pragmatic as Vico said: "the truth is to have made it".
In this paradigm, "sciences of the artificial" (see Herbert Simon) as cybernetics, automatics or decision theory, management and engineering sciences can justify their teaching and have a space in the academy as "real sciences".

Constructivism's concepts and ideas

Constructivism and sciences

Main article: Social constructionism Social constructivism in sociology

Constructivism and psychology

Main article: Constructivism (learning theory) Constructivism and education
For some, social constructionism can be seen as a source of the postmodern movement, and has been influential in the field of cultural studies. Some have gone so far as to attribute the rise of cultural studies (the cultural turn) to social constructionism.
On a realistic point of view, both postmodernism and constructivism can be seen as relativist theories.

Constructivism and postmodernism

Constructivist trends
Cultural constructivism asserts that knowledge and reality are a product of their cultural context, meaning that two independent cultures will likely form different observational methodologies. For instance, Western cultures generally rely on objects for scientific descriptions; by contrast, Native American culture relies on events for descriptions. These are two distinct ways of constructing reality based on external artifacts.

Cultural constructivism
Ernst von Glasersfeld is a prominent proponent of radical constructivism, which claims that knowledge is the self-organized cognitive process of the human brain. That is, the process of constructing knowledge regulates itself, and since knowledge is a construct rather than a compilation of empirical data, it is impossible to know the extent to which knowledge reflects an ontological reality.
See also: Francisco Varela, Humberto Maturana, and Heinz von Foerster

Radical constructivism
A series of articles published in the journal Critical Inquiry (1991) served as a manifesto for the movement of critical constructivism in various disciplines, including the natural sciences. Not only truth and reality, but also "evidence", "document", "experience", "fact", "proof", and other central categories of empirical research (in physics, biology, statistics, history, law, etc.) reveal their contingent character as a social and ideological construction. Thus, a "realist" or "rationalist" interpretation is subjected to criticism.
While recognizing the constructedness of reality, many representatives of this critical paradigm deny philosophy the task of the creative construction of reality. They eagerly criticize realistic judgments, but they do not move beyond analytic procedures based on subtle tautologies. They thus remain in the critical paradigm and consider it to be a standard of scientific philosophy per se.

Critical constructivism
James Mark Baldwin invented this expression, which was later popularized by Jean Piaget. From 1955 to 1980, Piaget was Director of the International Centre for Genetic Epistemology in Geneva.

Quotations

Anti-racist math
Deutsche Physik
Collective Simulations
Complexity
Constructivism (learning theory)
Constructivism in international relations
Family therapy
Irrealism
Metacognition
Personal construct psychology
Science and technology studies
Social constructionism
Systems theory
Teleology Proponents

Michael Devitt
David Kenneth Johnson
Robert Nola
Wal Suchting
David J. Weissman