Without renouncing the support of physics, it is possible for the physiology of the senses, not only to pursue its own course of development, but also to afford to physical science itself powerful assistance.
The presentations and conceptions of the average man of the world are formed and dominated, not by the full and pure desire for knowledge as an end in itself, but by the struggle to adapt himself favourably to the conditions of life.
The plain man is familiar with blindness and deafness, and knows from his everyday experience that the look of things is influenced by his senses but it never occurs to him to regard the whole world as the creation of his senses.
Physics is experience, arranged in economical order.
If our dreams were more regular, more connected, more stable, they would also have more practical importance for us.