Jean Piaget Research Paper

The core of Piaget’s theory is the conception of mind as an active system which, like an organism, assimilates external data into its structures and can adjust to these data. Special emphasis, in the knowledge process, is placed on the subject’s activity and the structures through which he or she perceives and understands things. Thus, the development of knowledge is viewed as the construction of new structures (rather than the accumulation of new information) triggered and guided by internal processes during the subject’s encounter with reality. Each new stage in this process opens up new possibilities. In this interactionist conception, structures are neither predetermined nor found in the environment and there are striking similarities between biological evolution, cognitive development in children, and the development of scientific thought.

1. Seven Decades Of Scientific Productivity

1.1 Childhood And Adolescence (1896–1918)

Jean Piaget was born in Neuchatel, a small city of Switzerland, on August 9, 1896. He was the son of an historian and professor of medieval literature at the university. Of his mother, he wrote in his autobiography that she was an intelligent and energetic woman, whose psychological imbalance created problems in the family. At the age of 11 years, Jean Piaget started classifying and collecting mollusks with the help of the director of the natural history museum of his hometown. In his teens, he was already an acknowledged specialist in the field and started publishing papers in scientific journals (as of 1911). This activity led him to decide to study natural sciences at the university between 1915 and 1918. At the same time, as of the age of 16 he became passionately interested in philosophy, and particularly in the theory of knowledge or epistemology. He soon decided to devote his life to the elaboration of a biological theory of knowledge, whose goal would be to explain the evolution of ideas both in individuals and in the scientific community. This project was influenced by evolutionary approaches in the field of biology (Lamarck, Darwin) and in philosophical works on issues of intelligence (Spencer, Le Dantec, Bergson). In the following years, Piaget’s professor of philosophy A. Reymond convinced him of the importance of a rationalist approach making use of logic and mathematics.

In 1918 Piaget published a philosophical and autobiographical novel (Recherche) describing the crisis he had gone through because of the conflict he felt between religion and science, or, in other words, between value and rationality. Eventually, the search for truth, which is the goal of science, became the most important value for Piaget. Recherche also contained the outline of a theory of the evolution of living and cognitive organizations based on the idea of improving forms of equilibrium between the whole and its parts. Piaget’s twofold interest on the one hand in biology and the associated problems of the organization and evolution of living beings, and on the other hand in epistemology and related issues concerning the validity of knowledge and its development, forms the basis of all his work.

1.2 Complementary Studies (1918–1921)

Piaget was convinced that a theory of knowledge should be validated by psychological research, and decided to get training in scientific psychology as soon as he graduated from university with his Ph.D. thesis on mollusks in 1918. He then spent a term in Zurich, attending courses in psychopathology—where he encountered psychoanalysis—and in experimental psychology. He then studied in Paris from 1919 to 1921, where he attended lectures in psychology (specifically by Janet), philosophy (with Lalande), and history of science (by Brunschvicg who had great influence on Piaget’s ideas). Courses in psychopathology provided him with a clinical interview method, which he soon used in his discussions with children. In effect, in parallel with his studies, he worked in the laboratory of Binet and Simon, standardizing intelligence tests for children. Piaget was fascinated by the reasoning of the children who did not yet answer ’correctly,’ and he discovered that the study of children’s thinking could be a means to validate a theory of knowledge. This program, which was to be the main focus of his work for 60 years, was very similar to the program designed by James Mark Baldwin (1861–1934), from whom Piaget borrowed several concepts and the expression ‘genetic psychology.’

1.3 The Early Psychological Research (1921–1929)

In 1921, Claparede offered a position in his Institute for educational sciences (known as the Jean-Jacques Rousseau Institute) in Geneva to Piaget, who was to conduct most of his professional life in this institution. What he found there were stimulating intellectual atmosphere and students willing to assist him in his work. Together with them the young researcher started a series of studies of children’s reasoning and soon published his first books: The Language and Thought of the Child (1923); Judgment and Reasoning (1924); The Child’s Conception of the World (1926); The Child’s Conception of Physical Causality (1927) (the titles given here and in the remainder of this text are the English translations of the French originals; the years are those of the original publications). The striking facts he discovered about the use of language, the nondifferentiation of concepts and the explanations of physical phenomena in children, as well as the detailed analyses and the synthetic categorization of these behaviors, brought Piaget almost immediate international fame. These studies showed that young children’s thinking is structurally and functionally different from that of older children and adults. Young children lack a true logic of classes and relations, they have difficulties viewing reality from an objective viewpoint, and they lack moral norms, which command compliance on the basis of a feeling of necessity. Children’s thinking tends to be egocentric, that is, they have difficulties in looking at things in perspective. In these early works, the passage from egocentric thought to a logical and more objective form of thinking was explained by a social factor: cooperation, or exchange between individuals who consider themselves as equals.

During this period, Piaget was involved in many activities beside his research. He taught child psychology at the J.-J. Rousseau Institute, philosophy and history of science at the University of Neuchatel (1925–1929), was for a few months psychoanalyzed by Sabina Spielrein, a pupil of Freud, and continued to study the evolution of mollusks. In 1923 he married a student at the Geneva Institute. Piaget and his wife Valentine spent much time minutely observing their three children who were born between 1925 and 1931. These observations were the basis of several books published in the following years.

1.4 Administrative Responsibilities, Professorship And New Directions Of Research (The 1930s)

In 1929, Piaget was appointed professor of history of science at the University of Geneva, where he subsequently became professor of sociology (1939) and of experimental psychology (after the death of Claparede, 1940). He also played an important administrative role at the J.-J. Rousseau Institute as associate director (1929), then as co-director (since 1932), reorganizing the Institute and establishing links between the Institute and the University. At the same time, and until the 1960s, he was director of the Bureau International de l’education and managed to convince the governments of many countries to join that organization.

Piaget’s most important activities continued to be research and writing. During these years, he accumulated data on children’s reasoning. However, apart from his book on moral judgment (1932)—simultaneously in French and in English—which was the sequel to the psychology books published in the 1920s, his major publications dealt with infant cognitive development. The choice of this topic stemmed from Piaget’s conviction that logic has its roots in actions and also from his deep interest in the issue of the origins of knowledge. The Origins of Intelligence (1936) and The Child’s Construction of Reality (1937) contained extremely original observations and explanations of infant behaviors, and departed radically from Piaget’s earlier writings as far as the explanatory model was concerned. Piaget discovered behaviors that had previously been overlooked, for example, the failure of babies younger than 9 months of age to look for an object hidden in front of them. Replications of these observations and experiments many years later around the world have confirmed these findings that had resulted from the observation of his three children.

In view of theory building, Piaget analyzed the elements of knowledge, the ‘schemes’ of actions, which become more differentiated and coordinated as development progresses. They evolve into increasingly complex and better-adapted forms of behavior, from automatic ‘reflexes’ to intelligent activities. This development is a special case of the relationship between the organism and the environment, in other words of biological adaptation. It results from the interaction between the subject of knowledge, who assimilates reality to his or her structures, and the object of knowledge, which may elicit an accommodation of these structures. Cognitive development is viewed as an evolving equilibrium between assimilation and accommodation. In The Child’s Construction of Reality (1937), Piaget studied the growth of the practical knowledge of object permanence, space, time, and causality in infants. He introduced a new and abstract explanatory notion: the mathematical concept of ‘group,’ which several authors in the social sciences considered as an interesting model at the time. Piaget applied it to the organization of spatial knowledge in infants and was convinced that it could be used to explain the logic of school-age children. To this end, from 1937 onwards, he worked for three years on this model, expressing it in algebraic formulae.

Although Piaget was now a famous author who had received an honorary degree from Harvard University in 1936, his two books on infant cognition were not translated in English until the 1950s. They contained too many abstract considerations and microanalyses and were definitely ahead of their time. A third book, also based on the observation of Piaget’s own children, was written during this period and published later: Play, Dream and Imitation (1945). It dealt with imitation in infants and the origins of symbolic thought in young children. Intellectual activity as well as play and imitation were defined in terms of equilibrium or disequilibrium between assimilation and accommodation.

1.5 The Mature Years: The Advent Of Structural Analysis (1940s)

During this and the following period, Jean Piaget was prodigiously productive, thanks to a strict and very regular work regime. In the mornings he would teach, discuss research with his large team of co-workers, and perform his administrative duties. Piaget would then spend the rest of the day mostly by himself. In the early afternoon, while thinking about the topics of his current writing, he would stroll or ride a bicycle in the countryside near Geneva. During the rest of the afternoon he would write, which was the best way for him to elaborate his ideas. Even when traveling or attending conferences he would not let a day go by without writing a few pages. Although he loved classical music he almost never went out in the evenings to movies, theaters or concerts. Both in summer and in winter, his love of nature led him to repeated sojourns in the mountains of the Valais, where he both hiked and worked.

The logical model of ‘grouping’ of mental operations, which he had recently developed, and which accounted for the organization of inferences in overall structures, inspired much research and writing. It permitted Piaget not only to describe the limitations of young children’s reasoning as he had done in his first books, but also to explain the sudden, stable, and rather generalized intellectual progress due to the advent of the elementary logic, of ‘concrete operations’. Between 1941 and 1948, his work resulted in six books: The Child’s Construction of Quantities (with B. Inhelder, 1941), The Child’s Conception of Number (with A. Szeminska, 1941), The Child’s Conception of Time (1946), The Child’s Conception of Movement and Speed (1946), The Child’s Conception of Geometry (with B. Inhelder and A. Szeminska, 1948), The Child’s Conception of Space (with B. Inhelder, 1948). These books study the elementary mastery of basic scientific concepts. This mastery, which usually emerges between the ages of 6 and 8 or 9 years, was explained in terms of the underlying ‘grouping’ structures that organize mental operations. This type of structure entails the reversibility of thinking, for Piaget an essential feature of natural logic. In contrast, younger children think that the number of a set of objects or the quantity of a substance change when spatial transformations occur, and that the duration of a movement corresponds to the distance covered, without taking into account the relative speed of the moving objects. These young children have difficulties comparing the number of elements in a subclass with the number in the superordinate class. As to space, geometrical capacities like inverting a spatial order, constructing a straight line with vertical sticks using a sighting method, and drawing the horizontal line of the water level in a tilted glass also usually emerge after the age of 7 years. The basic concept studied in each book was analyzed and defined in the light of children’s answers. For example, number was analyzed in terms of a synthesis between logical classification (class inclusion) and the seriation of asymmetrical relations (ordering by increasing or decreasing size); time was defined as the coordination of movements, in which the ability to consider speed played a fundamental role, and so forth.

Piaget also published a Treaty of Logic (1949) and with his co-workers he udied perception in children in the laboratory of experimental psychology. These studies, which attracted Piaget’s attention to the phenomenon of regulation, were to provide the subject matter of a much later book. The same holds true for the papers in sociology which were published during this decade and collected in a book called Sociological Studies in 1965.

The second World War rendered contact with foreign colleagues difficult, but Piaget was invited in 1942 to give a series of lectures in Paris at the ‘College de France’ (published in The Psychology of Intelligence, 1946). The abstract nature of his explanations struck many listeners as much as the brilliant analyses inspired by various scientific disciplines. After the war, UNESCO entrusted Piaget with several missions.

1.6 Achieving The Ultimate Goal Of His Work: The Elaboration Of A Genetic Epistemology (1950s)

In the 1950s, while continuing his work in genetic psychology with the help of his co-workers, Piaget devoted much of his effort to the foundation of a genetic epistemology, i.e., the study of the basic concepts and processes of the development of scientific knowledge. This used to be a topic of philosophical study but now became an object of scientific analysis. Actually, Piaget had indeed pursued epistemological issues throughout his entire previous work while ostentatiously focusing on the explanation of children’s thinking. Now he wished to discuss questions of knowledge per se as they were raised in the sciences (but continued to use the study of children’s cognitive development for this purpose). In 1950, Piaget published three volumes of an Introduction to Genetic Epistemology. The book begins with a general introduction defining genetic epistemology and its method and stating the main issues. Piaget develops an idea he had already expressed in earlier writings, that of a ‘circle of sciences’: physical reality is explained by mathematics, mathematics is the product of mind, which is a result of biological evolution, and organisms are closely connected with physical reality. The book deals in great detail with the epistemology of mathematics and physics, and in lesser detail with the epistemology of biology and the social sciences.

To make progress in the domain of genetic epistemology, Piaget founded the International Center for Genetic Epistemology, which was a working group comprising researchers in psychology and scientists from various disciplines (mathematics, physics, logic, etc.). The Center was launched in 1955 after obtaining, with difficulty, the necessary funding. A new series of books, which contained the results of the studies conducted at the Center for genetic epistemology, appeared from 1957 onwards. About 40 volumes were published in the series until the death of Piaget in 1980.

During the 1950s, when Piaget held a position as professor at the University of Paris (1952–1963), his psychological research in Geneva continued to progress and resulted in three books with B. Inhelder: The Development of Elementary Logical Structures (1959), a sequel to the studies of concrete operations; The Origin of the Idea of Chance (1951) and The Growth of Logical Thinking from Childhood to Adolescence (1955). The latter book provided a new description and definition of the highest stage of logical development: the formal operational stage achieved between the ages of 12 and 15 years. The formal model of the INRC group, derived from Klein’s mathematical group, provided an account of the new possibilities of reasoning which were available to adolescents. It involved a greater number of combinations of operations than the grouping structures (in particular a ‘double reversibility’ of thought). Moreover, the experiments by Inhelder showed how the understanding of physical phenomena developed in children and how, through the use of an adequate interview procedure, adolescents could rediscover fundamental scientific laws on their own.

1.7 The Last Two Decades (1960 To 1980): The Pinnacle Of Fame

Only in the late 1950s was Piaget’s work rediscovered by English and American psychologists, although he already had been a most respected professor and researcher in the French-speaking countries, and a well-known author in many other countries. During the following two decades he was among the most cited psychologists and best known scientists in the world. Most of his books were translated from French into foreign languages (a total of 24 different languages). From the end of the 1950s onwards, he received an increasing number of honorary degrees each year. When he died, he had received over 30 honorary degrees and several prestigious awards. However, these honors and the travels they involved did not prevent Piaget from continuing his work.

Until the beginning of the 1970s, studies of genetic epistemology mainly focused on problems related to logic, language, space, time, and causality. The latter topic—strangely neglected for several decades— proved difficult to study and remained on the program of the Center for Genetic Epistemology for several years in succession. On the whole, these books, while discussing issues specific to each science (e.g., the relative importance of time and speed in judgments about duration, or the possibility of geometrical intuition) validated the constructivist conception of Piaget’s epistemology. Effective forms of knowledge are neither innate nor drawn from the observation of the environment. They derive from the interaction of active individuals with their environment. A consequence of this position (summarized in the short book Genetic Epistemology, 1970) is that the rate of intellectual development can be only moderately accelerated by education. The goal of education, according to the few texts devoted by Piaget to this topic (for example a long article in 1965) is to favor children’s intellectual activity and their discovery of relationships and abstract concepts.

During the 1960s Piaget returned to his earliest field of interest: biology. He published a paper on the evolution of mollusks and about the reproduction of the ‘sedum’ plants, which he grew in his garden and observed carefully. In his book Biology and Knowledge (1967) he developed his ideas on biology and the parallel between biological and cognitive development. Simultaneously, he published three books on psychology. They dealt with the ‘figurative’ aspects of knowledge, whose function is to provide a kind of copy of things: The Mechanisms of Perception (1961), The Child’s Mental Imagery (1966), and Memory and Intelligence (1968). These books showed that figurative aspects are progressively subordinated to the subject’s operations: some optical illusions decrease with perceptual activity, and with the advent of logical thinking (concrete operations), mental images can adequately represent transformations, while memory of organized material improves. Intelligence is not captured by representation, i.e., a system of images or linguistic symbols; rather intelligence consists in operating on elements of reality or symbols and thus transforming them.

In the 1970s, after Piaget’s retirement as professor at the University of Geneva (1971), he continued his work with a large team of researchers at the Center for Genetic Epistemology. Most of his publications dealt with processes of cognitive development. For over 20 years, his main aim had been to demonstrate that efficient forms of knowledge result from structures that organize mental operations, and that these structures, which become increasingly complex over time, are rooted in biological organization. The time had come to deal with the processes involved in the construction of these structures, a topic that Piaget had neglected since the 1930s, except for a few epistemological papers written in the 1950s. During the last decade of his life, between the ages of 75 and 84 years, Piaget developed concepts that had been introduced earlier but needed fuller consideration and a precise definition: equilibration, reflexive abstraction, generalization, the opening up of new possibilities, and so on. These concepts are highly interesting and very original ideas, difficult to operationalize, but with deep and general explanatory value. Unfortunately, Piaget was so eager to continue his work that he changed the focus of his research and his writing nearly every year, although these complex concepts would deserve more sustained treatment.

Reflexive abstraction is the process through which something new is abstracted from experience. What is abstracted is not a property of the external world, but derives from the organization of the subject’s actions or operations. Equilibration is a self-regulation process, which is specific to living organizations. At the cognitive level, it is a reaction to an intellectual perturbation (such as a contradiction) which regulates the cognitive system and, in an attempt to compensate the perturbation, creates improved forms of knowledge. For his eightieth birthday in 1976, a kind of dissertation defense was organized: Piaget defended the theses developed in The Equilibration of Cognitive Structures (1975) before a ‘jury’ composed of famous scientists who represented different disciplines. In this last period, Piaget’s work also dealt with the grasp of consciousness, contradiction, and dialectics. He explored the relevance to the explanation of cognition of the mathematical concept of morphism and of the idea of logic of meaning. The last work was conducted in collaboration with R. Garcia who was also co-author of Psychogenesis and History of Science (published posthumously in 1983). Piaget also dealt with problems of biology. His post-Lamarckian ideas attributed some importance to aspects of experience in the evolution of species (for example in Behavior, a Motor of E olution, 1976).

1.8 Factors Of Scientific Creativity

Piaget died on September 16, 1980, leaving behind a life’s work of unusual scope, in terms of depth, originality, interdisciplinary relevance, and volume. The explanation of his exceptional scientific productivity is not only the conjunction of a brilliant mind with a great capacity for work, but also the stimulation of reflection by the results of constantly renewed research. It was also due to Piaget’s sociability, which enabled him to easily convince others to work with him; and to a strong sense of a mission to which everything else was subordinate. According to Piaget, having a theory to contradict was a powerful stimulus. The dominant empiricist conceptions in psychology—neo-associationism—and logical positivism in philosophy played this role well into the 1960s. Since the mid-1960s, Piaget was busy developing arguments against the relatively widespread idea, prevalent since Chomsky published his work, that important aspects of knowledge are innate.

2. The Importance Of Piaget’s Work For The Social Sciences

Piaget’s theory is exceptionally comprehensive, as it gives a detailed account of cognition from birth to adolescence, and also deals with scientific knowledge in adults. It contains an incredible wealth of experimental data covering these periods in life, especially the age range from 5 to 9 years. It deals with fundamental problems often ignored in other psychological theories, such as the relationship between biological activity and cognition, the relative role of the subject and the environment, and the connections between different aspects of cognition such as perception, reasoning, and memory. In some respects Piaget’s work was ahead of its time and it could therefore easily establish connections with emerging disciplines such as cybernetics (since the mid-1940s) and, later, artificial intelligence. The concepts of selfregulated systems and of feedback specific to cybernetics were involved, less explicitly, in the Piagetian ideas of reversible structures (present in his work at least since 1937) and of the regulation of cognitive activities (frequently referred to by him in the early 1940s). The artificial intelligence programs which expressed in symbolic language the expertise involved in the mastery of a task bear some resemblance to the Piagetian concept of repeatable action schemes and recall Piaget’s attempts to formalize mental structures. Moreover, the multidisciplinary approach known as cognitive science, which emerged in the 1980s, is completely in line with Piaget’s approach, with its links between biology, psychology, logic, and physics.

One aspect of Piaget’s work, genetic epistemology, which is focused on scientific knowledge as investigated through studies of children, has had little impact outside of Geneva. By contrast, Piaget’s psychological work has definitely influenced subsequent orientations and research in the social sciences.

Since the 1920s, Piaget’s findings about the reasoning of children had considerable influence on child psychology. The influence was strong in the 1960s and 1970s, in particular regarding the four successive stages of cognitive development, (sensorimotor, preoperational, concrete operational, and formal operational). In fact, Piaget’s idea was not to define general stages of child development, but necessary steps in the integration of new forms of knowledge. His detailed findings concerning the emergence of new capacities, such as the search for hidden objects in babies, conservation of quantity in school-age children, and combinatory operations in adolescents remain useful landmarks of psychological development although they cannot be used as psychometric tests. During the same two decades, various experiments in education were directly inspired by aspects of the theory, namely the role of the child’s activity and the importance attributed to general structuring abilities rather than specific learning. However, mainstream psychology and education, especially in English-speaking countries, often remained im- pervious to Piaget’s influence, except for the growth of cognitive developmental psychology.

Cognitive developmental psychology became a productive subdiscipline of psychology, especially since the beginning of the 1970s. Practically every developmental psychologist in the world at that time had at least some knowledge of Piaget’s work and the very idea of studying cognitive development using a cross-sectional method was inspired by the work previously undertaken in Geneva. Piaget’s writing often played the same role of a ‘theory to contradict’ that associationism or nativist conceptions had played for Piaget. Many authors in developmental psychology launched their careers by conducting experiments that were designed to prove Piaget wrong. Because his constructivist conceptions grant a limited role to social influence, and in particular to education, they were unacceptable to many. Much research has been performed especially in the USA to show that cognitive competencies existed in children well before the ages indicated by Piaget. In order to demonstrate this, the problems presented to the children were modified and compared to those presented by Piaget himself. The race for early competencies in the 1980s and 1990s gave rise to the idea that many cognitive capacities were innate. In the end, Piaget’s conceptions were not followed, but thanks to his work a whole field of psychology developed.

Piaget’s work paved the way for the cognitivist revolution in psychology, from the mid-1960s onwards. Psychologists had become interested in mental states, a taboo for many decades due to the predominant behaviorist conception. The new generation of psychologists could read in Piaget’s work detailed studies of mental states that had been conducted over a period of several decades.

At the end of the twentieth century, Piaget’s theory had indirect descendants in the fields of child psychology, cognitive science, and developmental psychology. Ideas of specialists in educational science are more directly inspired by Piaget’s work, especially in French-speaking countries and in Latin America. Studies in moral development also derive directly from Piaget’s research in this field. More generally, constructivist approaches which attribute importance to the activity of the subject, in applied psychology as well as in other disciplines, usually refer, albeit vaguely at times, to the work of the Swiss psychologist and epistemologist.

Bibliography:

1. Bringuier J-C 1989 Conversations with Jean Piaget. University of Chicago Press, Chicago
2. Ducret J-J 1990 Jean Piaget: biographie et parcours intellectuel. Delachaux Nestle, Neuchatel, Switzerland
3. Gruber H, Voneche J (eds.) 1995 The Essential Piaget. Aronson, London
4. Inhelder B, Piaget J 1955 De la logique de l’enfant a la logique de l’adolescent. P.U.F., Paris. [English translation, 1972 The
5. Growth of Logical Thinking From Childhood to Adolescence. Routledge, London]
6. Montangero J, Maurice-Naville D 1992 Piaget ou l’intelligence en marche. Vocabulaire et apercu chronologique. Mardaga, Liege, Belgium [English translation, 1997. Piaget or the Advance of Knowledge. Glossary and Chronological Overview. Erlbaum, Mahwah, NJ]
7. Piaget J 1926 La representation du monde chez l’enfant. Alcan, Paris [English translation 1972 The Child’s Conception of the World. Littlefield Adams, Totowa, NJ]
8. Piaget J 1932 Le jugement moral chez l’enfant. Alcan, Paris [English translation 1977 The Moral Judgment of the Child. Penguin, Harmondsworth, UK]
9. Piaget J 1936 La naissance de l’intelligence chez l’enfant. Delachaux and Nestle, Neuchatel, Switzerland [English translation 1970 The Origins of Intelligence. Routledge, London]
10. Piaget J 1945 La formation du symbole chez l’enfant. Delachaux and Nestle, Neuchatel, Switzerland [English translation 1962 Play, Dreams and Imitation. Norton, New York]
11. Piaget J 1967 Biologie et connaissance. Gallimard, Paris [English translation 1971 Biology and Knowledge. The University of Chicago Press, Chicago]
12. Piaget J 1970 L’epistemologie genetique. P.U.F., Paris [English translation 1972 The Principles of Genetic Epistemology. Routledge, London]
13. Piaget J 1970 reedited Psychologie et epistemologie. Denoel, Paris [English translation 1971 Psychology and Epistemology. Grossman, New York]
14. Piaget J 1972 reedited Problemes de psychologie genetique. Denoel, Paris [English translation 1973 The Child and Reality: Problems of Genetic Psychology. Grossman, New York]
15. Piaget J 1972 Ou a l’education. Denoel-Gonthier, Paris [English translation 1973 To Understand is to Invent: the Future of Education. Grossman, New York]
16. Piaget J 1975 L’equilibration des structures Cognitives. P.U.F., Paris [English translation 1985 The Equilibration of Cognitive Structures The University of Chicago Press, Chicago]
17. Piaget J 1981 Le possible et le necessaire 2 Vols. P.U.F., Paris [English translation 1987 Possibility and Necessity. University of Minneapolis Press, Minneapolis, MN
18. Piaget J, Inhelder B 1941 Le Developpement des quantites chez l’enfant. Delachaux and Nestle, Neuchatel, Switzerland [English translation 1974 The Child’s Construction of Quantities. Routledge, London]
19. Piaget J, Inhelder B 1948 La representation de l’espace. P.U.F., Paris [English translation 1967 The Child’s Conception of Space. Norton, New York]
20. Piaget J, Inhelder B 1968 Memoire et intelligence. P.U.F., Paris [English translation 1973 Memory and Intelligence. Basic Books, New York]
21. Vidal F 1994 Piaget before Piaget. Harvard University Press, Cambridge, MA