The difficulty with customary psychological explanation is that it breaks the reflex arc of the nervous system into three parts whose relations are successive and causal rather than simultaneous and organic. There is not first a stimulus, then perception, then response; these processes are supplementary, not separate. Or, from another point of view, psychological explanation must begin with a whole process which, when analyzed, is seen to contain the three moments or phases: stimulus, sensation, and response. The whole process is primary and actual, the abstracted phases are secondary and derivative. With the disappearance of the mechanical interpretation of the perceptual process, mental states vanish. Representative perceptionism is thus done away with, together with all the problems which it generates. The position of conscious, or reflective thought, in Dewey's scheme, is especially interesting. This mode of thought is not constantly operative, but arises only in situations of stress and strain, when habitual modes of response break down. A dualism is established between reflective thought and the habitual life processes. Dewey does not take the ground that these processes are supplementary, as he had done in the case of stimulus, sensation, and response. It will be remembered that Dewey had defined judgment, in his logical and ethical writings of an earlier period, as a special activity operating in critical situations. This conception of judgment is now carried over into his psychology, and given a biological basis. It is worth noting that this view of judgment was worked out in logical terms before it was reinforced by biological data. Nevertheless, it is through biology that Dewey is able to give his interpretation of the thought process that empirical concreteness which he demanded from the beginning, but achieved very slowly. The value of the functional psychology, considered merely as psychology, is undeniable. It is, in fact, a natural and almost inevitable step in the development of psychological theory. Dewey's achievement consists in the establishment of an organic mode of interpretation in psychology, intended to displace the mechanical interpretation. The mechanical causal series is displaced by an organic system of internally related parts. Dewey, however, does not display any interest in the logical aspects of his doctrine. He takes the biological situation literally, as a fact empirically given, and to be accepted without criticism. A discussion of the period now under consideration would not be complete without reference to certain articles which supplement the essay discussed above. The first of these is an article on "The Psychology of Effort," published in the _Philosophical Review_ in 1897.[123]