Possibility and Necessity was first published in 1987. Minnesota Archive Editions uses digital technology to make long-unavailable books once again accessible, and are published unaltered from the original University of Minnesota Press editions.

This two-volume work—Jean Piaget''s last—was published in France in 1981 and 1983 and is available now for the first time in English translation. Reflecting the preoccupations and methodologies of his later years, Possibility and Necessity combines theoretical interpretation with detailed summaries of the experiments Piaget and his colleagues used to test their hypotheses.

Volume 2 presents a series of experiments documenting the way children between the ages of four or five and eleven to thirteen come to develop a grasp of necessity and its role in understanding the world about them. The experiments show how children proceed from an initial level (at four or five years) of pseudo-necessities, where they see the world as necessarily what it appears to be without the existence of other possibilities, to an intermediate level (at six to ten years), where pseudo-necessities give way to increasingly rich arrays of possibilities, and a final stage (at eleven to thirteen years), where children are able to select among these multiple possibilities the one that fits all the data. This stage represents the optimal level of understanding reality, which is now seen by the child as infinitely variable yet coherent and lawful. Psychologically, this lawfulness corresponds to a sense of necessity, or certainty.

Volume 2 thus completes the theory presented in Volume 1 (The Role of Possibility in Cognitive Development) by showing how cognitive development is mediated on the one hand by a dialectical process of ever-expanding possibilities and, on the other, by increasingly delimiting necessities. In demonstrating how this process operates in psychological development—and in pointing out analogies in the history of science — Piaget gave his genetic epistemology its final and most accomplished form. The acquisition of knowledge is thus shown to be the result of two complementary processes: the formation of possibilities and the grasping of necessary laws and constraints in the construction of a reasoned representation of the external world.