The psycho-physiological hypothesis is both inductively and deductively the sine qua non of the science of psychology.

Human institutions depend for their existence and stability on the impulse of self-preservation and its close associate, - the fear instinct.

Superstitions, and especially the early cultivation of religion, with its "fear of the Lord" and of unknown mysterious agencies, are especially potent in the development of the instinct of fear. Even the early cultivation of morality and conscientiousness, with their fears of right and wrong, often causes psychoneurotic states in later life. Religious, social, and moral taboos and superstitions, associated with apprehension of threatening impending evil, based on the fear instinct, form the germs of psychopathic affections.

The general tendency of evolution is from structure to function, from bondage to freedom of the individual elements.

The tendency of life is not the preservation of the species, but solely the preservation of each individual organism, as long as it is in existence at all, and is able to carry on its life processes.

Not purpose but chance is at the heart of mental life.

Social laughter is momentary, soon burns itself out and passes away like the fire and smokes of straw, but genius shakes the very skies with its lasting, inextinguishable laughter.