gation. If we are to consider the relations between science and engineering, the relation between pure and applied science will have first to be made very clear; and for this purpose we shall need working definitions. Once stated, these definitions may seem an elaboration of the obvious and an oversimplification. But the elaboration often seems obvious only after it has been stated, and the definitions may have to be simple in order to bring out the necessary distinctions. By "pure science" or "basic research" is meant a method of investigating nature by the experimental method in an attempt to satisfy the need to know. Many activities in pure science are not experimental, as, for instance, biological taxonomy; but it can always be shown that in such cases the activities are ancillary to experiment. In the case of biological taxonomy the classifications are of experimental material. Taxonomy is practiced in other areas where it is not scientific, such as in the operation of libraries. By "applied science" is meant the use of pure science for some practical human purpose. Thus science serves two human purposes: to know and to do. The former is a matter of understanding, the latter a matter of action. Technology, which began as the attempt to satisfy a practical need without the use of science, will receive a fuller treatment in a later section.