[The question for the behavioral disciplines is simply] what is better, and how do we get there? - Kenneth E. Boulding

An international system consists of a group of interacting behavior units called "nations" or "countries," to which may sometimes be added certain supra-national organizations, such as the United Nations. Each of the behavior units in the system can be described in terms of a set of "relevant variables." Just what is relevant and what is not is a matter of judgment of the system-builder, but we think of such things as states of war or peace, degrees of hostility or friendliness, alliance or enmity, arms budgets, geographic extent, friendly or hostile communications, and so on. Having defined our variables, we can then proceed to postulate certain relationships between them, sufficient to define a path for all the variables through time. Thus we might suppose, with Lewis Richardson that the rate of change of hostility of one nation toward a second depends on the level of hostility in the second and that the rate of change of hostility of the second toward the first depends on the level of hostility of the first. Then, if we start from given levels of hostility in each nation, these equations are sufficient to spell out what happens to these levels in succeeding time periods.

The human being, on the other hand, is firmly located in a temporal process. He has an image of the past which extends back far beyond the limits of his own life and experience, and he likewise has an image of the future. Closely associated with the time structure of his image is the image of the structure of relationships. Because we are aware of time, we are also aware of cause and effect, of contiguity and succession, of cycles and repetition. The image of man is also characterized by a much greater degree of self-consciousness and of self-awareness than that of the lower animals. We not only know, but we know that we know. This reflective character of the human image is unique, and is what leads to philosophy.

It is almost as hard to define mathematics as it is to define economics, and one is tempted to fall back on the famous old definition attributed to , “Economics is what economists do,” and say that mathematics is what mathematicians do. A large part of mathematics deals with the formal relations of quantities or numbers.