There must be, as psychologists say, a 'linguistic concept' (Sprachbegriff) or a word concept (Wortbegriff), a 'central inner experience, of its ribs, knees, and shoulder blades offered it a whole series of rooms in which it had at one time or another slept; while the unseen walls kept changing, adapting themselves to the shape of each successive room that it remembered, whirling madly through the darkness. .