Nel, after throwing a stone onto a sloping bank watching the stone rolling said, 'Look at the stone. It's afraid of the grass - Jean Piaget

I … sent a program of research to the Rockefeller Foundation. … [Their] questions were almost all of a surprising pertinence. I remember the practical questions … But I particularly remember the theoretical questions, due among others to [Shannon] Weaver, the mathematician interested in information theory who was then in charge of the Department of Science at the Foundation: How will you find interesting epistomological ideas, for example, the theory of relativity, in studying children who know nothing and who in any case are brought up in the intellectual tradition dating from Newton? …

I had the luck to be able to remark … that Einstein himself had advised me in 1928 to study the formation of the intuitions of velocity in order to see if they depended on those of duration, and that further, when I had the good fortune to see Einstein again at Princeton …, he was quite delighted by the reactions of nonconservation of children of four to six years (they deny that a liquid conserves its quantity when it is poured from one glass into another of a different shape: ‘There is more to drink than before,‘ etc.), and was greatly astonished that the elementary concepts of conservation were only constructed toward seven or eight years.

Classical logic believed it was possible to discover the actual structure of thought processes, and the general structures underlying the external world as well as the normative laws of the mind . . . As logic has perfected its formal rigor, logicians have ceased to interest themselves in the study of actual thought processes.

Knowledge is not predetermined by heredity; it is not predetermined in the things around us - in knowing things around him the subject always adds to them.