Existentialism: Those who adopt an existential posture typically express the conviction that human beings can never be certain of anything beyond the sheer fact of their own existence. What human beings assert that they know is wholly capricious and unreliable. The subjective quality of the process of knowing is seen by the existentialist as inevitable. […]

Intuition: The idea of mysticism can be defined as the belief that the most reliable source of knowledge or truth is intuition rather than reason, sense experience, or the scientific method. The mystic maintains that immediate and true knowledge is attained through a direct awareness that does not depend on systematic mental activity or sense impressions. […]