Talcott Parsons( 1937)
In the first chapter attention was called to the fact that in the process of scientific conceptualization concrete phenomena come to be divided into units or parts. The first salient feature of the conceptual scheme to be dealt with lies in the character of the units which it employs in making this division. The basic unit may be called the "unit act." Just as the units of a mechanical system in the classical sense, particles, can be defined only in terms of their properties, mass, velocity, location in space, direction of motion, etc., so the units of action systems also have certain basic properties without which it is not possible to conceive of the unit as "existing." Thus, to continue the analogy, the conception of a unit of matter which has mass but which cannot be located in space is, in terms of the classical mechanics, nonsensical. It should be noted that the sense in which the unit act is here spoken of as an existent entity is not that of concrete spatiality or otherwise separate existence, but of conceivability as a unit in terms of a frame of reference. There must be a minimum number of descriptive terms applied to it, a minimum number of facts ascertainable about it, before it can be spoken of at all as a unit in a system.
In this sense then, an "act" involves logically the following: (1) It implies an agent, an "actor." (2) For purposes of definition the act must have an "end," a future state of affairs toward which the process of action is oriented. (3) It must be initiated in a "situation" of which the trends of development differ in one or more important respects from the state of affairs to which the action is oriented, the end. This situation is in turn analyzable into two elements: those over which the actor has no control, that is which he cannot alter, or prevent from being altered, in conformity with his end, and those over which he has such control. The former may be termed the "conditions" of action, the latter the "means." Finally (4) there is inherent in the conception of this unit, in its analytical uses, a certain mode of relationship between these elements. That is, in the choice of alternative means to the end, in so far as the situation allows alternatives, there is a "normative orientation" of action. Within the area of control of the actor, the means employed cannot, in general, be conceived either as chosen at random or as dependent exclusively on the conditions of action, but must in some sense be subject to the influence of an independent, determinate selective factor, a knowledge of which is necessary to the understanding of the concrete course of action. What is essential to the concept of action is that there should be a normative orientation, not that this should be of any particular type. As will be seen, the discrimination of various possible modes of normative orientation is one of the most important questions with which this study will be confronted. But before entering into the definition of any of them a few of the major implications of the basic conceptual scheme must be outlined.
The first important implication is that an act is always a process in time. The time category is basic to the scheme. The concept end always implies a future reference, to a state which is either not yet in existence, and which would not come into existence if something were not done about it by the actor or, if already existent, would not remain unchanged. This process, seen primarily in terms of its relation to ends, is variously called "attainment," "realization," and "achievement."____________________