Jean Piaget, the Swiss psychologist whose study of child development has often been compared to Freud's work in its vast influence on the science of human intelligence, died in Geneva today. He was 84 years old. Dr. Piaget was hospitalized 10 days ago at Geneva Cantonal Hospital. He is survived by three children. The cause of death was not disclosed. The question to which Jean Piaget addressed himself was deceptively obvious and simple: How does a child learn? His answer, often phrased in obtuse language, was in brief that a child learns by discrete stages related to age and that he is a significant agent in the process. His stress on the interaction of biological functions and the structure of the environment, elaborated in more than 60 years of research, was, in the opinion of many psychologists and education specialists, as liberating and as revolutionary as Sigmund Freud's earlier insights into the stage development of human emotional life. Many hailed him as one of the century's most creative scientific thinkers. And indeed Dr. Piaget's theories exercised a profound effect on thinking about children in Europe and America. They have basically altered man's perceptions of the mechanism and functioning of his intelligence. Educators seized upon his work. In contrast to the traditional views of how we acquire knowledge--that heredity plays a dominant role or that environmental factors are controlling--Dr. Piaget proposed that each child, starting from birth, constructs and reconstructs his very own model of reality, of the world about him, in a regular sequence. He does this through a multitude of direct experiences with persons and objects, in the course of which cognitive growth takes place not merely by amassing new facts. The child's transformation of these experiences into conceptions is constantly revised through his own self- discoveries, which tend to eliminate errors in previous conceptions. A simple example of this phenomenon was cited recently by Dr. David Elkind of Tufts University, a Piaget specialist. He wrote: "The child of 3 or 4 already has an elementary concept of quantity: confronted with two identical glasses of orangeade filled to the same level, he would say that both had the 'same to drink.' But if the orangeade from one glass were poured into a tall, narrow beaker while he looked on, the child would say, Piaget found, that the tall glass had 'more to drink' than the shorter one. "Not until about 6 or 7 do most children understand that changing the shape of a quantity does not change the amount. The young child has a concept of quantity, but it is clearly a different concept from the one held by older children and adults: he thinks the amount of liquid can be gauged by its level without taking its width into account. Older children and adults, however, assess liquid quantities by taking both height and width into consideration. "This is mental growth by integration, wherein a new, higher-level idea (amount is determined by height and width) is formed by the integration of two lower-level ideas (amount is determined by height or width). It suggests that mental growth is an expanding upward spiral in which the same problems are attacked at successive levels but are resolved more completely and more successfully at each higher level." In addition, Dr. Piaget explained that mental growth takes place by integration of diverse concepts and replacement or primitive notions of nature by more mature ideas with age. Thus, very young children tend to believe that the sun and the moon follow them around, a notion that is replaced in later years. Four major stages of mental growth were delineated by Dr. Piaget, based on the cognitive tasks accomplished in each. In the sensory-motor period--the initial two years of life--the child is chiefly concerned with the mastery of objects, blocks, large toys, rocks, household objects and the like. From 2 to 6, his main concern is with symbols such as those in language, fantasy, dreams and play. For about the next five or six years, or until age 12, the child learns to master numbers, relations and classes and how to reason about them. Finally, in the three years to age 15, he is occupied with the mastering of purely logical thought, and he can think about his own thinking and that of others. The continuum, in Dr. Piaget's presentation, is quite complex, yet each stage has its telltale characteristics. A number of hardy theories were challenged by Dr. Piaget's work: that a child is a little adult; that ideas are inborn; that learning takes place by environmental conditioning or reinforcement; that the young child is capable of absorbing facts as they are understood by adults; and that he copies the world about him. In place of these notions, Dr. Piaget sought to substitute what he called genetic epistemology. In this concept, the timetable that appears to underlie the development of intellectual skills indicates that the capacity for logical thought is coded, along with sex, eye color and the shape of the nose, in the genes. Rational tendencies, however, do not mature simply because they are innate; rather, they grow with use. The application of this theory in education stresses the importance of what is called the "discovery method" of teaching, in which a child gets an opportunity to apply his developing abilities and test their limitations. The teacher is a guide, not a force-feeder of ready-made truths. "The goal of education is not to increase the amount of knowledge but to create the possibilities for a child to invent and discover, to create men who are capable of doing new things," Dr. Piaget explained. Dr. Piaget's early discoveries with children gained him worldwide acclaim in the 20 and 30's, but after that his works were considered too remote from the dominant trends in American behavioral science. Then in the late 50's and early 60's he was rediscovered. In the last few years most of his basic works have been translated and several explications for the general reader have been published. The most accessible of Dr. Piaget's own works are "Six Psychological Studies" and "The Psychology of the Child;" books about him include "Understanding Piaget," "The Essential Piaget" and "An Outline of Piaget's Developmental Psychology for Students and Teachers." Along with an enthusiasm for Dr. Piaget in some American academic and educational circles there has been criticism. Traditionalists objected to the radical way he conceived of the child's task of acquiring knowledge. And many sympathetic with Dr. Piaget's overall interpretation feel alternative interpretations can be put forth for many of the phenomena he uncovered. Other critics also argued that his theory offered little help in clarifying the motivations and accomplishments of individual children. Many critics, however, agreed with Robert Coles of Harvard that Dr. Piaget had focused psychologists' attention on "man the developing thinker rather than on man the universal neurotic." Tall, portly and rumpled-looking in his bulky suits, Dr. Piaget resembled a magnified Einstein, an impression that was accented by his bushy white hair. Out of doors he covered part of this unruly mane with a navy blue beret. To many who met him, according to Professor Elkind, Dr. Piaget gave off "an aura of intellectual presence not unlike the aura of a dramatic presence emanated by a great actor." Smoking a meerschaum and chatting with friends--and especially with children--he seemed benign and gracious, but members of his staff in Geneva knew that he could also be aloof and remote. For years he followed a strict schedule. Up at 4 A.M., he wrote at least four publishable pages in a small, even hand. Later, he taught classes or attended meetings. After lunch he walked and pondered whatever problem faced him. "I always like to think on a problem before reading about it," he said. And in the evening he read. In the summer he departed to an Alpine retreat to talk, meditate and write. Apart from articles and lectures, his output totaled more than 50 books and monographs. Several of them, including "The Child's Conception of Space" and "The Growth of Logical Thinking From Childhood to Adolescence," were written with Barbel Inhelder, his longtime associate at the Institute of Educational Science in Geneva. Dr. Piaget's road to child psychology started with a youthful interest in zoology. The son of specialist on the Middle Ages, he was born Aug. 9, 1896, in Neuchatel, Switzerland. Something of a prodigy, he published articles on mollusks in scientific journals by the age of 15. At 22 he was granted a doctoral degree with a thesis on mollusk distribution in the Valais Alps. He became interested also in psychology, attending lectures by Carl Jung. From these and his own speculations, he recalled, he became "haunted by the idea of discovering a sort of embryology of intelligence." This was the basis for his later idea that life could be understood best in terms of "structures of the whole." In 1920 he went to Paris to work with Theodore Simon, a co-developer with Alfred Binet of an intelligence test for children. Scrutinizing responses to the test questions, Dr. Piaget believed he saw a pattern in the wrong answers, a pattern that related to a child's age group. This finding led him to investigate the children's world, including the crib activities of his own three youngsters. Possessed of a remarkable empathy with children, he spent long hours on his hands and knees shooting marbles with them, exploring their notions of space, ethics, numbers and the like. From these observations came his first book, "The Language and Thought of The Child," which traced the development of child's speech from egocentric to socialized forms. His researches in psychology spanning over a half-century built up an impressive body of insights. His basic approach was to get inside of the child's mind and see the world through its eyes. "I engage my subjects in conversation," Dr. Piaget recounted, "patterned after psychiatric questioning, with the aim of discovering something about the reasoning underlying their right but especially their wrong answers." Among other things, he found that "children not only reasoned differently from adults, but also that they had quite different world views, literally different philosophies." For example, he noted that in a child's view "objects like stones and clouds are imbued with motives, intentions and feelings." The mind is thus not a passive mirror but an active artist as it develops increasingly sophisticated versions of reality. The unfolding of Dr. Piaget's explanations occurred over a lifetime, so there were refinements as new evidence was sifted; but these did not alter his basic theories. The elaboration of these was institutionalized in the International Center for Genetic Epistemology that he established in Geneva in 1955 with funds from the Rockefeller Foundation. In his mature years Dr. Piaget was widely acclaimed. There were honorary degrees from dozens of universities, including Oxford and Harvard, and impressive guest appearances at scholarly meetings. He remained, however, a remote public figure--more the distant philosopher than the polemicist.