In the first place, it may be assumed that all of man's activity furthers some general end, as, for instance, the maintenance of life. Then man's activity may be viewed as a sequence of acts, which tend to further this end, and on this basis we may separate out stimulus and response. "It is only when we regard the sequence of acts _as if_ they were adapted to reach some end that it occurs to us to speak of one as stimulus and the other as response. Otherwise, we look at them as a _mere_ series."[120] In these cases the stimulus is as truly an act as the response, and what we have is a series of sensory-motor coordinations. Looking, for instance, is a sensory-motor coordination which is the stimulus or antecedent of another coordinated act, running away. The first coordination passes into the second, and the second may be viewed as a modification or reconstitution of the first. But this external teleological distinction between sensation and response is not so important as the distinction now to be made. So far only fixed coordinations, habitual modes of action, have been considered. But there are situations in which habitual responses and fixed modes of action fail: situations in which new habits are formed. In these situations there arises a special distinction between stimulus and response, for in these formative situations the stimuli and responses are consciously present in experience as such. "The circle is a coordination, some of whose members have come into conflict with each other. It is the temporary disintegration and need of reconstitution which occasions, which affords the genesis of, the conscious distinction into sensory stimulus on one side and motor response on the other."[121] The distinction which arises between stimulus and response is a distinction of function within the problematical situation. Suppose that a sound is heard, the character of which is uncertain, and which, as a coordination, does not readily pass into its following coordination, or habitual response. The sound is puzzling, and moves into the center of attention. It is fixed upon, abstracted, studied on its own account. In that event, the sound may be spoken of as a sensation. As a sensation, it is the datum of a reflective process of thought, or conscious inference, whose aim is to constitute the sound a stimulus, or, in other words, to find what response belongs to it. When this response is determined the problem is done with and sensory-motor unity is achieved.