Certain American psychologists employ the term _imageless thought_ to designate abstract concepts. The expression is liable to be misunderstood. It should not be construed as excluding all concomitance and concurrence of sensible imagery, in relation to the process of thought. What is really meant is that sensible appearances do not make up the sum-total of our internal experiences, but that we are also aware of mental acts and states which are not reducible to imagery. In other words, we experience thought; and thought and imagery, though concomitant, are not commensurable. The clarity and coherence of thought does not depend on the clarity or germaneness of the accompanying imagery, nor is it ever adequately translatable into terms of that imagery. Thus the universal triangle of geometry, which is not right, nor oblique, nor isosceles, neither scalene nor equilateral, neither large nor small, neither here nor there, neither now nor then, is not visualizable in terms of concrete imagery, although we are clearly conscious of its significance in geometrical demonstrations. Imagery differs according to the person, one man being a visualist, another an audist, another a tactualist, another a motor-verbalist, etc. But thought is the same in all, and consequently it is thought, and not imagery, which we convey by means of speech. Helen Keller, whose imagery is mainly motor and tactile, can exchange views with an audist or visualist on the subject of geometry, even though the amount of imagery which she has in common with such persons is negligible. “_Eine Bedeutung_,” says Bühler, “_kann man überhaupt nicht vorstellen, sondern nur wissen_,” and Binet, in the last sentence of his “L’Étude expérimentale de l’intelligence,” formulates the following conclusion: “Finally—and this is the main fact, fruitful in consequences for the philosophers—the entire logic of thought escapes our imagery.”