Contractile movements arise, sometimes at the instigation of external stimuli but sometimes also in the absence of any apparent external influence.

Psychology, on the other hand, seeks to give account of the interconnexion of processes which are evinced by our own consciousness, or which we infer from such manifestations of the bodily life in other creatures as indicate the presence of a consciousness similar to our own.

The animal kingdom exhibits a series of mental developments which may be regarded as antecedents to the mental development of man, for the mental life of animals shows itself to be throughout, in its elements and in the general laws governing the combination of the elements, the same as the mental life of man.

Some say that everything that is called a psychical law is nothing but the psychological reflex of physical combinations, which is made up of sensations joined to certain central cerebral processes... It is contradicted by the fact of consciousness itself, which cannot possibly be derived from any physical qualities of material molecules or atoms.

Physiology seeks to derive the processes in our own nervous system from general physical forces, without considering whether these processes are or are not accompanied by processes of consciousness.

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

The old metaphysical prejudice that man 'always thinks' has not yet entirely disappeared. I am myself inclined to hold that man really thinks very little and very seldom.