50

“Nothing is more practical than a good theory,” the famous phrase attributed to Kurt Lewin claims. And yet, if a theory is to be applied in practice, it is crucial that it does not meet with too many obstacles along the way, as was the case when psychology practitioners were considered, from a Marxist perspective, to be participating in the alienation of the workers. This will be my first point. The second is another case in which external circumstances had an influence, this time positive, on the link between theory and practice: the creation of postgraduate psychology diplomas with a specialization in “childhood and adolescence.” My third and main point will be a brief account of the repeated failure of a practice—the measurement of intelligence in infants—owing to a lack of sufficient reflection on the successive theories to which this practice has appealed. Finally, I shall conclude this exploration of the tortuous relations between theory and practice with a detour by way of the necessary popularization and promotion of our theories.