The opposite of such a zigzag course is a train of thought such as an argument. In a train of thought, one general idea prescribes the direction, or forms the “subject,” or limits what has been called the universe of discourse. Attention is wholly guided by the general idea, and refuses to be distracted by any interest or suggestion which does not bear upon it. Let the general idea be, for example, the relation of wealth to the best life. Experience shows that it is most difficult to resist the varied interests and distractions which present themselves in the attempt to keep this relation in view. Easy and attractive modes of acquisition, easy and attractive modes of expenditure, force themselves upon the mind as isolated {164} suggestions, and divert it from the question: “Shall I, or will any one else, be the better for it, as I understand better?” The effort of control, needed to keep in view the general nature of our conception of what is best in life, and to attend to suggestions which offer themselves as to acquisition and expenditure, only in so far as they seem likely to promote that conception, means the predominance of a scheme or general idea through all the varied circumstances of economic possibility. It makes no difference whether we are speaking of reasoning or of practice. The nature of the control which insists on relevancy, and of the intellectual system in which it exhibits itself, is the same in both cases. Every mind, in fact, is more or less organised under the control of dominant ideas, which belong to its habitual preoccupations and determine the constant bias of its thoughts. There is a well-known story how a traveller in a railway carriage undertook to detect the vocation of each of his fellow travellers from their respective answers to a single question. The question was: “What is that which destroys what it has itself produced?” and a naturalist, so the story runs, revealed himself by the answer, “vital force,” a soldier replied “war,” a scholar “Kronos,” a journalist “revolution,” and a farmer “a boar.” [1] Each answer was determined by the dominant bias or idea which selected out of the possible answers to the riddle that which would harmonise with the general mental system under its control. Selection, it must be remembered, is at the same time creation. In every situation, {165} theoretical or practical, the surroundings as a whole are new, and the rule or scheme has to assert itself in conditions which are not precisely repeated from any former case. In so asserting itself it does not simply _reproduce_ something old, any more than a batsman recalls a former movement when he plays a ball, but it _produces_ that thought or deed which expresses its nature with reference to the new surroundings in which it has to act. [2] For it is a universal tendency, a scheme partly defined, and in process of further defining itself by moulding the material presented to it. [1] Steinthal, in James’ _Psychology_, II., 108.