But while the characteristics of what is popularly known as the scientific mind are not peculiar to scientific men, it is true that, in their actual scientific work, these characteristics have a greater survival value than they possess in almost any other kind of work. The extent to which mental habits may be local, confined to some only of a man’s mental activities, has been made apparent by the war. The majority of men’s minds are split up into water-tight compartments in a way truly astonishing, and the various eloquent addresses on the moral value of scientific studies now make melancholy reading. We must assume of scientific men, as of any other class, that such qualities of fairness and deliberation as they exhibit in their work are imposed upon them as conditions of success, and are not, in general, the natural manifestations of an exceptionally delicate moral sensibility. If we adopt William James’ classification of human beings into tender-minded and tough-minded the dividing line runs through the scientific camp as through any other. We see this most clearly in the case of mathematicians, for idealist or empiricist assumptions seem to be equally reconcilable with the results. Such sciences as physics and chemistry seem, at first glance, to be given over to the tough-minded; the official language, as it were, is the language of the tough-minded, but directly controversy arises on a point having philosophical bearings we see the dichotomy establish itself. Nevertheless, it remains true that while scientific men, as human beings, are of all sorts, they do exhibit, in their own work, a degree of mental honesty which is unusual. It is easy to see that this virtue, at any rate, has a strictly utilitarian basis. A scientific man is honest because he cannot succeed on any other terms in the long run. The experimental verification always looms ahead. He cannot, like the mystic who maintains his opinion in face of the world, take refuge in the deeper insight. His results are communicable and verifiable or they are not science. Philosophies may be constructed which no man can verify and no man can refute. Their authors may, with complete assurance, remain satisfied of their truth and lament the universal blindness of mankind, just as a poet may present a front of unconquerable self-esteem to the ignorant derision of the world. But the whole claim of science is that it is communicable and capable of verification. It is found, as a matter of experience, that results of this kind are not usually obtained unless a certain mental habit is first acquired. It is this mental habit which is usually called the scientific mind. Where it is the outcome of a natural predisposition it may be classed as a moral quality, and, as such, is not peculiar to, or widely distributed amongst, scientific men. But as a tool, as a kind of technique, it is of more obvious value and is more extensively employed in the sciences than in any other human activities.