But, Dewey says, modern logicians tend to disregard judgment as act, and pay attention to it only as content. The generic ideas are studied in independence of their applications, as if this were a matter of no concern in logic. "In truth, there is no such thing as control of one content by mere reference to another content as such. To recognize this impossibility is to recognize that the control of the formation of the judgment is always through the medium of an act by which the respective contents of both the individual judgment and of the universal proposition are selected and brought into relationship to each other."[207] The individual act of judgment is necessary to logical theory, because the act of the individual forms the connecting link between the generic idea and the specific details of the situation. There must be some means whereby the instrumental concept is brought to bear upon its appropriate material. "The logical process includes, as an organic part of itself, the selection and reference of that particular one of the system which is relevant to the particular case. This individualized selection and adaptation is an integral portion of the logic of the situation. And such selection and adjustment is clearly in the nature of an act."[208] This problem of the relation of the categories to their subject-matter is an acute one for Dewey, because of limitations placed upon thought. He decides that the idea must be, in some fashion, self-selective, must signify its own fitness to a given subject-matter. But it can only be self-selective by being itself in the nature of an act. It turns out that the generic idea has been evolved in connection with acts of judgment, and its own applicability is born in it. "The activity which selects and employs is logical, not extra-logical, just because the tool selected and employed has been invented and developed precisely for the sake of just such future selection and use."[209] The logic and system of science must be embodied in the individual. He must be a good logical medium, his acts must be orderly and consecutive, and generic ideas must have a good motor basis in his organism, if he is to think successfully. This is the essence of Dewey's argument in the essay under discussion. The inference seems to be that logic cannot be separated from biology and psychology, since the act of knowing and the ideas which it employs have a physiological basis.