There are other sources of psychological knowledge, which become accessible at the very point where the experimental method fails us.

Our mind is so fortunately equipped, that it brings us the most important bases for our thoughts without our having the least knowledge of this work of elaboration. Only the results of it become unconscious.

Experimental psychology itself has, it is true, now and again suffered relapse into a metaphysical treatment of its problems.

The materialistic point of view in psychology can claim, at best, only the value of an heuristic hypothesis.

Hence, even in the domain of natural science the aid of the experimental method becomes indispensable whenever the problem set is the analysis of transient and impermanent phenomena, and not merely the observation of persistent and relatively constant objects.

Hence, wherever we meet with vital phenomena that present the two aspects, physical and psychical there naturally arises a question as to the relations in which these aspects stand to each other.

The task of physiological psychology remains the same in the analysis of ideas that it was in the investigation of sensations: to act as mediator between the neighbouring sciences of physiology and psychology.