"A scheme is the structure or the organization of actions which is transferred
or generalized when this action is repeated in similar or analogous circum-
stances" ( The Psychology of the Child, [ 1966] 1969, footnote not translated in
the English version, p. 11 ) or: "The scheme of an action is neither perceptible
(one perceives a particular action, but not its scheme) nor directly in-
trospectible, and we do not become conscious of its implications except by
repeating the action and comparing its successive results" ( Mathematical
Epistemology and Psychology, [ 1961] 1966, p. 235). These definitions are
followed by numerous examples of sensorimotor, verbal, operatory, and
affective schemes and internalized actions.

One of Piaget's major preoccupations was the analysis of the development
of knowledge explained by the concept of equilibration, whose definition and
history the present volume clarifies with examples galore. The authors have
not stopped at this conceptualization of cognitive progression; rather, they
have also included the last set of concepts, which throws a light on:

A mechanism that leads from intra-object (object analysis) to inter-object
(analyzing relations or transformations) to trans-object (building of structures)
levels of analysis. That this dialectical triad can be found in all domains and at
all levels of development seems to us to constitute the principal result of our
comparative effort. In fact, the generality of this triplet, intra, inter, and trans,
and its occurrence at all sublevels as well as within global sequences undoubtedly
constitutes the best of the arguments in favor of a constructivist epistemology.
( Psychogenesis and the History of Science, [ 1983], 1989, p. 28-29)

I am equally happy to note that the authors not only refer to Piaget's most
recent works, but also to the "Etudes d'épistémologie génétique," which are
usually less known. The many analyses and quotations to be found in the
present volume are closely linked thanks to a very clear historical study that
is mainly based on Piaget's books on psychology, on which the authors offer
their personal perspective.

To end this brief foreword I would like not only to congratulate the authors
for their pertinent and meticulous piece of work, but also to say that I envy
young students, researchers, and interpreters of Piaget's work, for they now
have such a valuable tool at their disposal.

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