Psychological Types by C. G. Jung (1921) - Translation by H. Godwyn Baynes (1923)

Intuition
(From intueri = to look into or upon) is, according to my view, a basic psychological function (v. Function). It is that psychological function which transmits perceptions in an unconscious way. Everything, whether outer or inner objects or their associations, Can be the object of this perception.

Intuition has this peculiar quality: it is neither sensation, nor feeling, nor intellectual conclusion, although it may appear in any of these forms. Through intuition anyone content is presented as a complete whole, without our being able to explain or discover in what way this content has been arrived at Intuition is a kind of instinctive apprehension, irrespective of the nature of its contents.

Like sensation (q.v.) it is an irrational (q.v.) perceptive function. Its contents, like those of sensation, have the character of being given, in contrast to the 'derived' or 'deduced' character of feeling and thinking contents.

Intuitive cognition, therefore, possesses an intrinsic character of certainty and conviction which enabled Spinoza to uphold the 'scientia intuitiva' as the highest form of cognition.[61]

Intuition has this quality in common with sensation, whose physical foundation is the ground and origin of its certitude. In the same way, the certainty of intuition depends upon a definite psychic matter of fact, of whose origin and state of readiness, however, the subject was quite unconscious.

Intuition appears either in a subjective or an objective form: the former is a perception of unconscious psychic facts whose origin is essentially subjective; the latter is a perception of facts which depend upon subliminal perceptions of the object and upon the thoughts and feelings occasioned thereby.

Concrete and abstract forms of intuition may be distinguished according to the degree of participation on the part of sensation. Concrete intuition carries perceptions which are concerned with the actuality of things, while abstract intuition transmits the perceptions of ideational associations. Concrete intuition is a reactive process, since it follows directly from the given circumstances; whereas abstract intuition, like abstract sensation, necessitates a certain element of direction, an act of will or a purpose.

In common with sensation, intuition is a characteristic of infantile and primitive psychology. As against the strength and sudden appearance of sense-impression it transmits the perception of mythological images, the precursors of ideas (q.v.).
Intuition maintains a compensatory function to sensation, and, like sensation, it is the maternal soil from which thinking and feeling are developed in the form of rational functions. Intuition is an irrational function, notwithstanding the fact that many intuitions may subsequently be split up into their component elements, whereby their origin and appearance can also be made to harmonize with the laws of reason.

Everyone whose general attitude is orientated by the principle of intuition, i.e. perception by way of the unconscious, belongs to the intuitive type [62] (v. Type).

According to the manner in which intuition is employed, whether directed within in the service of cognition and inner perception or without in the service of action and accomplishment, the introverted and extraverted intuitive types can be differentiated.

In abnormal cases a well-marked coalescence with, and an equally great determination by, the contents of the collective unconscious declares itself: this may give the intuitive type an extremely irrational and unintelligible appearance.