Jean Piaget's (1896-1930) research program about human knowledge counts as one of the major contributions to psychology and epistemology because it has translated philosophical questions into empirical ones, setting a standard against which any new paradigm about the nature and growth of knowledge is still measured today. Hence its pertinence for cognitive sciences because, like them, Piaget departed from the limited aims of psychology to discover the most general principles of cognition.
Piaget's basic idea is that knowledge continues biological ADAPTATION by different means. This means that intelligence is considered as a sort of organ and, as such, has both a functional side and a structural one. But, whereas other organs have fixed structures and fixed functions, cognitive organs present a functional continuity within structural discontinuities. The functional continuity is the emergence and growth of knowledge during evolution. Structural discontinuities are the different forms knowledge takes during the course of the growth of a species, a culture, or an individual. These discontinuities are marked by a stage like construction of successive invariants ensuring a certain stability to the world in which the organism lives (homeostasis).
Such a position is called constructivism in epistemology, because it is a sort of midway between two opposites: realism and nominalism. REALISM pretends that things exist independently of their instances in the actual world by necessity. Such a view secures the objectivity and universality of knowledge. Nominalism considers that what we call things are mere conveniences that vary according to one's needs and conventions. This relativistic approach accounts for the variability of things according to cultural changes. As one can see, constructivism being both fixed in its functional dimension and ever changing in its structural one solves the opposition gracefully without reducing one perspective to the other or excluding one in favor of the other.
The rest of Piaget's program characterizes the sequences and mechanisms by which rational knowledge develops.
Sequences of development are marked by a constant abstraction of conservation from the mere permanence of objects to the laws of conservation in physics and chemistry. In order for the world to acquire the minimum stability requested to retrieve an object once it has disappeared from perception, space must be conceived as a container within which all the moves of an observer form a mathematical group of displacements. Then time, matter, weight, and volume need to be conserved first in action, symbols, and concepts, as well as logical classes, relations, and numbers, on the logico-mathematical side.
Conservation accounts for the preservation of knowledge at each level of development but not for the acquisition of new knowledge. This is made possible by novelty or the attainment of better knowledge and by necessity or the interconnection of all available knowledge into logically necessary systems.
Novelty plays an important role in Piaget's theorizing. First, the emergence of novelty in knowledge is considered by him as evidence in favor of his constructivistic view and against the two extreme positions in the nature-nurture dilemma. NATIVISM and environmentalism both exclude novelty because it is mere unfolding in nativism and a matter of learning in environmentalism. Second, the sudden emergence of novelty proves the stage like nature of the growth of knowledge. But, third and above all, novelty changes the face of knowledge both in the child and in science. Once a child has discovered that, when one gets the concept of number, all the numerical operations will yield a number and nothing else but a number ad infinitum, this novel knowledge changes the child's outlook of the world in the very same way that the discovery of object permanence makes the baby search for objects that have disappeared and abandon the "out of sight out of mind" attitude so typical of newborns. In science, the double movement of geometrization of physics and physicalization of space accomplished by Albert Einstein when he applied Georg Riemann's geometry to gravity modified completely the way physicists looked at the world. Thus progress in cognition both generates and is generated by novelty.
But novelty is not enough. Knowledge needs to be true knowledge (novelty) and knowledge of the truth (necessity). This could not be explained only in terms of an interaction between nature and nurture because how could mere contigencies generate necessity? Piaget offers a more general factor: equilibration, subsuming nature and nurture, under one explanatory system transcending them in levels of generality, necessity, and abstraction. To understand the abstract nature of equilibration, let us suppose that living organisms are governed by the second law of thermodynamics. If this is so, then the resulting increase in entropy of the system cannot be considered as either innate or acquired but as depending on a law of probability. In the very same way, equilibration is the law of development, an abstract necessary principle independent of any contingencies and resulting in an endless optimization of living systems (homeorhesis) in a stage like sequence considered as the ideal course of evolution or chreode.
A number of criticisms have been raised against Piaget's psychological points: age of attainment, neuropsychological mechanisms of concept acquisition, etc. These criticisms have unfortunately confused Piaget's epistemological points that are essential to his theory with psychological ones that are contingent and thus open to change for him too, because they were just algorithms.
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