ASSOCIATION IN THINKING.--All thinking proceeds by the discovery or recognition of relations between the terms or objects of our thought. The science of mathematics rests on the relations found to exist between numbers and quantities. The principles and laws of natural science are based on the relations established among the different forms of matter and the energy that operates in this field. So also in the realm of history, art, ethics, or any other field of human experience. Each fact or event must be linked to other facts or events before it possesses significance. Association therefore lies at the foundation of all thinking, whether that of the original thinker who is creating our sciences, planning and executing the events of history, evolving a system of ethics, or whether one is only learning these fields as they already exist by means of study. Other things being equal, he is the best thinker who has his knowledge related part to part so that the whole forms a unified and usable system. ASSOCIATION AND ACTION.--Association plays an equally important part in all our motor responses, the acts by which we carry on our daily lives, do our work and our play, or whatever else may be necessary in meeting and adapting ourselves to our environment. Some sensations are often repeated, and demand practically the same response each time. In such cases the associations soon become fixed, and the response certain and automatic. For example, we sit at the table, and the response of eating follows, with all its complex acts, as a matter of course. We lie down in bed, and the response of sleep comes. We take our place at the piano, and our fingers produce the accustomed music. It is of course obvious that the influence of association extends to moral action as well. In general, our conduct follows the trend of established associations. We are likely to do in great moral crises about as we are in the habit of doing in small ones. 2. THE TYPES OF ASSOCIATION FUNDAMENTAL LAW OF ASSOCIATION.--Stated on the physiological side, the law of habit as set forth in the definition of association in the preceding section includes all the laws of association. In different phrasing we may say: (1) Neurone groups accustomed to acting together have the tendency to work in unison. (2) The more frequently such groups act together the stronger will be the tendency for one to throw the other into action. Also, (3) the more intense the excitement or tension under which they act together the stronger will be the tendency for activity in one to bring about activity in the other.