I came across this folk story at a testing blog, "Know Enough to be Dangerous":

The Three Tradesmen

A great city was besieged, and its inhabitants were called together to consider the best means of protecting it from the enemy.

• A Bricklayer earnestly recommended bricks as affording the best material for an effective resistance.
• A Carpenter, with equal enthusiasm, proposed timber as a preferable method of defense.
• Upon which a Currier stood up and said, "Sirs, I differ from you altogether: there is no material for resistance equal to a covering of hides; and nothing so good as leather."

Every man for himself.

Rather than "Every man for himself," I would say "Every man from himself." That is, it refers to individuals' (and theorists') chains of experience that constrain their ability to think and learn, much like my son's interpreting situations in terms of his own experience, and again showing the viability of radical constructivism as a theory.

von Glasersfeld, drawing upon Piaget, was the architect of radical constructivism. According to this theory,

• Knowledge is not passively received either through the senses or by way of communication;
• Knowledge is actively built up by the cognizing subject;
• The function of cognition is adaptive, in the biological sense of the term, tending towards fit or viability;
• Cognition serves the organization of the experiential world, not the discovery of ontological reality. (Radical Constructivism: A Way of Knowing and Learning, 1995, p. 51)

These four principles refute that notion that one can access--or make progress toward increasingly accurate representations of--objective reality or truth. Rather, we simply construct models and revise those models as we interact with our environment. So, radical constructivists use the term "viability" to represent how well one's models fit one's experiences with the environment. For this reason, "good" teaching results from the ability to listen to one's students and respond to them in ways that help them construct viable models for their school experiences.

Similarly, "good" theory building results from the ability to listen to other theorists and respond to them in ways that helps one create a new model that is perceived to fit our experiences better than our previous models.