In Psychological Types, Jung maintained that the functioning of the human psyche entails four basic forms of activity. These functions cannot be reduced to each other and are invariant relative to the specific content of experience, which changes from moment to moment. The four functions of which Jung spoke are thinking, feeling, sensing, and intuition. Jung viewed thinking and feeling as diametrically opposed to each other and as “rational.” That is, both are representational functions; they involve a reflection on, and an (e)valuation of, externally experienced reality from the inner perspective of the subject. In the case of thinking, the subjective base is abstract and disembodied (e.g., discursive reasoning, logical deduction, mathematical calculation), while, in the case of feeling, it is more concrete and embodied (I value what lies outside me in terms of the likes and dislikes of my body).

Beyond these “rational” operations lie the “irrational” functions of sensing and intuition, also seen to make up a pair of opposites. Irrational activity can be characterized as more “presentational” than representational; that is, it entails a more immediate (less reflective) reaching out to, grasping, and taking in of that which is other in the field of experience. In sensory perception, we experience the world discretely, dividing the objects we encounter into units that are bounded from each other. On the other hand, intuiting the world means apprehending it as an undivided whole, as in cases of “hunches” or “visions,” where we are seized by a nebulous impression about the general course of events but are unable to account for the source of the presentiment. While the irrational functions are attenuated in adulthood, being constricted by the ascendant influence of rational thinking, according to Jung these functions originate in an “infantile and primitive psychology” that serves as the “matrix out of which thinking and feeling develop as rational functions.” Evidently, intuition would be the most primal form of experience, for while sensation involves “perception via conscious sensory functions,” intuition entails “perception by way of the unconscious,” through “dreams and fantasies,” through a mode of operating in which one surrenders oneself “wholly to the lure of possibilities.”