"What is thus said of a special group of inquiries by one of the foremost of the younger psychologists, is not without its bearings on all the departments in which psychology can learn. For physiological, or what is technically called psychological, experiment, is co-ordinate with many other sources of information. Much, for instance, is to be learnt by a careful study of language by those who combine sound linguistic knowledge with psychological training. It is in language, spoken and written, that we find at once the great instrument and the great document of the distinctively human progress from a mere Psycheto a mature Nous, from Soul to Mind. Whether we look at the varieties of its structure under different ethnological influences, or at the stages of its growth in a nation and an individual, we get light from language on the differentiation and consolidation of ideas. But here again it is easy to lose oneself in the world of etymology, or to be carried away into the enticing questions of real and ideal philology."