Inhelder in her introduction. The reason for this unity is that explanatory adequacy can be attained only by exploring the formative and constructive aspects of development. To explain a psychologic reaction or a cognitive mechanism (at all levels, including that of scientific thought) is not simply to describe them, but to comprehend the processes by which they were formed; failing that, one can but note results without grasping their meaning. JEAN PlACET VI Man distinguishes himself from other creatures primarily by his abstract reasoning capacity and his ability to communicate his...