Psychology must postulate uniformity of interrelation of physical, physiological, and psychic processes. - Boris Sidis

Psychology is the science of psychic states both as to content and form, regarded from an objective standpoint, and brought in relation to the living corporeal individual.

The fact that psychology postulates an external material world and studies it in so far as it comes to be reflected in consciousness, points to another postulate which psychology must assume in addition, namely, the existence of an inner world consciousness.

If ceaseless vigilance is the price of liberty, more so is it true that ceaseless criticism of ever new opinions and ever new views, however distasteful, bizarre, and paradoxical, is the price of truth.