Cognitive functions, also referred to as psychological functions, as described by Carl Jung in his book Psychological Types, are particular mental processes within a person's psyche that are present regardless of common circumstance. This is a concept that serves as one of the foundations for his theory on personality type. In his book, he noted four main psychological functions: thinking, feeling, sensation and intuition. He introduced them with having either an internally focused (introverted) or externally focused (extraverted) tendency which he called "attitudes". He also categorizes the functions as either rational (thinking and feeling) or irrational (intuition and sensation). Psychological functions and attitudes The four psychological functions may be subjugated to the control of consciousness, which can take two attitudes: Extraversion: "a strong, if not exclusive, determination by the object." Consciously, in an extravert, the four basic cognitive functions follow the extraverted 'general attitude of consciousness': "Now, when the orientation to the object and to objective facts is so predominant that the most frequent and essential decisions and actions are determined, not by subjective values but by objective relations, one speaks of an extraverted attitude. When this is habitual, one speaks of an extraverted type. If a man so thinks, feels, and acts, in a word so lives, as to correspond directly with objective conditions and their claims, whether in a good sense or ill, he is extraverted." Introversion: "a turning inwards of the libido, whereby a negative relation of subject to object is expressed. Interest does not move towards the object, but recedes towards the subject." Consciously, in an introvert, the four basic cognitive functions follow the introverted 'general attitude of consciousness'. "Everyone whose attitude is introverted thinks, feels, and acts in a way that clearly demonstrates that the subject is the chief factor of motivation while the object at most receives only a secondary value." The difference between extraversion and introversion comes from the source of the decisive factor in forming motivation and developing ideas, whether it is objective (i.e. the external environment) or subjective (experienced within the mind, or "processes inherent in the psyche"). When discussing function types, Jung ascribed movements of the libido in both directions for each function in each function type, but with one direction being that final judge. To summarize Jung's views, as discussed in Psychological Types and maintained until his death, Jung posited that each individual follows a "general attitude of consciousness"