The importance of this remarkable work deserves to be doubly emphasized, for its novelty consists both in the results obtained and in the method by which they have been reached. How does the child think. How does he speak. What are the characteristics of his judgment and of his reasoning. For half a century the answer has been sought to these questions which are those which we meet with at the very threshold of child psychology. If philosophers and biologists have bent their interest upon the soul of the child, it is because of the initial surprise they experienced at his logic and speech. In proof of this, we need only recall the words of Taine, of Darwin and of Egger, which are among the first recorded in the science of child logic.