I was reading this thread and wanted to respond. But after writing this I thought about making it a completely different thread. So if anyone has any expanding thoughts to this OP please Id like to hear them.

To answer the question asked in the linked thread, I would say we use our functions. The functions are basic mental processes that we all use over the course of a day.

I will now quote some items from Jung Lexicon because I cant seem to make it sound better than that.

Function. A form of psychic activity, or manifestation of libido, that remains the same in principle under varying conditions. (See also auxiliary function, differentiation, inferior function, primary function and typology.)

Jung's model of typology distinguishes four psychological functions: thinking, feeling, sensation and intuition.

"Sensation establishes what is actually present, thinking enables us to recognize its meaning, feeling tells us its value, and intuition points to possibilities as to whence it came and whither it is going in a given situation."["A Psychological Theory of Types," CW 6, par. 958.]

Though all the functions exist in every psyche, one function is invariably more consciously developed than the others, giving rise to a one-sidedness that often leads to neurosis.

"The more [a man] identifies with one function, the more he invests it with libido, and the more he withdraws libido from the other functions. They can tolerate being deprived of libido for even quite long periods, but in the end they will react. Being drained of libido, they gradually sink below the threshold of consciousness, lose their associative connection with it, and finally lapse into the unconscious. This is a regressive development, a reversion to the infantile and finally to the archaic level. . . . [which] brings about a dissociation of the personality."[The Type Problem in Aesthetics," ibid., pars. 502f.]

Primary function. The psychological function that is most differentiated. (Compare inferior function.) In Jung's model of typology, the primary or superior function is the one we automatically use because it comes most naturally.

"Experience shows that it is practically impossible, owing to adverse circumstances in general, for anyone to develop all his psychological functions simultaneously. The demands of society compel a man to apply himself first and foremost to the differentiation of the function with which he is best equipped by nature, or which will secure him the greatest social success. Very frequently, indeed as a general rule, a man identifies more or less completely with the most favoured and hence the most developed function. It is this that gives rise to the various psychological types."[Definitions," CW 6, par. 763.]

In deciding which of the four functions-thinking, feeling, sensation or intuition-is primary, one must closely observe which function is more or less completely under conscious control, and which functions have a haphazard or random character. The superior function (which can manifest in either an introverted or an extraverted way) is always more highly developed than the others, which possess infantile and primitive traits.

"The superior function is always an expression of the conscious personality, of its aims, will, and general performance, whereas the less differentiated functions fall into the category of things that simply "happen" to one."[General Description of the Types," ibid., par. 575.]

Auxiliary function. A helpful second or third function, according to Jung's model of typology, that has a co-determining influence on consciousness.

"Absolute sovereignty always belongs, empirically, to one function alone, and can belong only to one function, because the equally independent intervention of another function would necessarily produce a different orientation which, partially at least, would contradict the first. But since it is a vital condition for the conscious process of adaptation always to have clear and unambiguous aims, the presence of a second function of equal power is naturally ruled out. This other function, therefore, can have only a secondary importance. . . . Its secondary importance is due to the fact that it is not, like the primary function . . . an absolutely reliable and decisive factor, but comes into play more as an auxiliary or complementary function."["General Description of the Types," CW 6, par. 667.]

The auxiliary function is always one whose nature differs from, but is not antagonistic to, the superior or primary function: either of the irrational functions (intuition and sensation) can be auxiliary to one of the rational functions (thinking and feeling), and vice versa.

Thus thinking and intuition can readily pair, as can thinking and sensation, since the nature of intuition and sensation is not fundamentally opposed to the thinking function. Similarly, sensation can be bolstered by an auxiliary function of thinking or feeling, feeling is aided by sensation or intuition, and intuition goes well with feeling or thinking.

"The resulting combinations [see figure below] present the familiar picture of, for instance, practical thinking allied with sensation, speculative thinking forging ahead with intuition, artistic intuition selecting and presenting its images with the help of feeling-values, philosophical intuition systematizing its vision into comprehensive thought by means of a powerful intellect, and so on."[Ibid., par. 669.]

Type Combinations

Inferior function. The least differentiated of the four psychological functions. (Compare primary function.)

"The inferior function is practically identical with the dark side of the human personality."["Concerning Rebirth," CW 9i, par. 222.]

In Jung's model of typology, the inferior or fourth function is opposite to the superior or primary function. Whether it operates in an introverted or extraverted way, it behaves like an autonomous complex; its activation is marked by affect and it resists integration.

The inferior function secretly and mischievously influences the superior function most of all, just as the latter represses the former most strongly.["The Phenomenology of the Spirit in Fairytales," ibid., par. 431.]

Positive as well as negative occurrences can constellate the inferior counter-function. When this happens, sensitiveness appears. Sensi-tiveness is a sure sign of of the presence of inferiority. This provides the psychological basis for discord and misunderstanding, not only as between two people, but also in ourselves. The essence of the inferior function is autonomy: it is independent, it attacks, it fascinates and so spins us about that we are no longer masters of ourselves and can no longer rightly distinguish between ourselves and others["The Problem of the Attitude-Type," CW 7, par. 85.]

The inferior function is always of the same nature, rational or irrational, as the primary function: when thinking is most developed, the other rational function, feeling, is inferior; if sensation is dominant, then intuition, the other irrational function, is the fourth function, and so on. This accords with general experience: the thinker is tripped up by feeling values; the practical sensation type gets into a rut, blind to the possibilities seen by intuition; the feeling type is deaf to logical thinking; and the intuitive, at home in the inner world, runs afoul of concrete reality.

One may be aware of the perceptions or judgments associated with the inferior function, but these are generally over-ridden by the superior function. Thinking types, for example, do not give their feelings much weight. Sensation types have intuitions, but they are not motivated by them. Similarly, feeling types brush away disturbing thoughts and intuitives ignore what is right in front of them.

Although the inferior function may be conscious as a phenomenon its true significance nevertheless remains unrecognized. It behaves like many repressed or insufficiently appreciated contents, which are partly conscious and partly unconscious . . . . Thus in normal cases the inferior function remains conscious, at least in its effects; but in a neurosis it sinks wholly or in part into the unconscious. ["Definitions," CW 6, par. 764.]

To the extent that a person functions too one-sidedly, the inferior function becomes correspondingly primitive and troublesome. The overly dominant primary function takes energy away from the inferior function, which falls into the unconscious. There it is prone to be activated in an unnatural way, giving rise to infantile desires and other symptoms of imbalance. This is the situation in neurosis.

In order to extricate the inferior function from the unconscious by analysis, the unconscious fantasy formations that have now been activated must be brought to the surface. The conscious realization of these fantasies brings the inferior function to consciousness and makes further development possible.[Ibid., par. 764.]

When it becomes desirable or necessary to develop the inferior function, this can only happen gradually.

I have frequently observed how an analyst, confronted with a terrific thinking type, for instance, will do his utmost to develop the feeling function directly out of the unconscious. Such an attempt is foredoomed to failure, because it involves too great a violation of the conscious standpoint. Should the violation nevertheless be successful, a really compulsive dependence of the patient on the analyst ensues, a transference that can only be brutally terminated, because, having been left without a standpoint, the patient has made his standpoint the analyst. . . . [Therefore] in order to cushion the impact of the unconscious, an irrational type needs a stronger development of the rational auxiliary function present in consciousness [and vice versa].["General Description of the Types," ibid., par. 670.]

Attempts to assimilate the inferior function are usually accompanied by a deterioration in the primary function. The thinking type can't write an essay, the sensation type gets lost and forgets appointments, the intuitive loses touch with possibilities, and the feeling type can't decide what something's worth.

And yet it is necessary for the development of character that we should allow the other side, the inferior function, to find expression. We cannot in the long run allow one part of our personality to be cared for symbiotically by another; for the moment when we might have need of the other function may come at any time and find us unprepared. ["The Problem of the Attitude-Type," CW 7, par. 86.]

Typology. A system in which individual attitudes and behavior patterns are categorized in an attempt to explain the differences between people.

Jung's model of typology grew out of an extensive historical review of the type question in literature, mythology, aesthetics, philosophy and psychopathology. Whereas earlier classifications were based on observations of temperamental or physiological behavior patterns, Jung's model is concerned with the movement of energy and the way in which one habitually or preferentially orients oneself in the world.

First and foremost, it is a critical tool for the research worker, who needs definite points of view and guidelines if he is to reduce the chaotic profusion of individual experiences to any kind of order. . . . Secondly, a typology is a great help in understanding the wide variations that occur among individuals, and it also furnishes a clue to the fundamental differences in the psychological theories now current. Last but not least, it is an essential means for determining the "personal equation" of the practising psychologist, who, armed with an exact knowledge of his differentiated and inferior functions, can avoid many serious blunders in dealing with his patients.["Psychological Typology," ibid., par. 986.]

Jung differentiated eight typological groups: two personality attitudes-introversion and extraversion-and four functions-thinking, sensation, intuition and feeling, each of which may operate in an introverted or extraverted way.

Introversion and extraversion are psychological modes of adaptation. In the former, the movement of energy is toward the inner world. In the latter, interest is directed toward the outer world. In one case the subject (inner reality) and in the other the object (things and other people, outer reality) is of primary importance.

[Introversion] is normally characterized by a hesitant, reflective, retiring nature that keeps itself to itself, shrinks from objects, is always slightly on the defensive and prefers to hide behind mistrustful scru-tiny. [Extraversion] is normally characterized by an outgoing, candid, and accommodating nature that adapts easily to a given situation, quickly forms attachments, and, setting aside any possible misgivings, will often venture forth with careless confidence into unknown situations. In the first case obviously the subject, and in the second the object, is all-important.["The Problem of the Attitude-Type," CW 7, par. 62. ]

The crucial factor in determining whether one is introverted or extraverted, as opposed to which attitude is currently operative, is not what one does but rather the motivation for doing it-the direction in which one's energy naturally, and usually, flows.

Whether a person is predominantly introverted or extraverted only becomes apparent in association with one of the four functions, each with its special area of expertise: thinking refers to the process of cognitive thought, sensation is perception by means of the physical sense organs, feeling is the function of subjective judgment or valuation, and intuition refers to perception via the unconscious.

Briefly, the sensation function establishes that something exists, thinking tells us what it means, feeling tells us what it's worth, and through intuition we have a sense of its possibilities.

In this way we can orient ourselves with respect to the immediate world as completely as when we locate a place geographically by latitude and longitude. The four functions are somewhat like the four points of the compass; they are just as arbitrary and just as indispen-sable. Nothing prevents our shifting the cardinal points as many degrees as we like in one direction or the other, or giving them differ-ent names. It is merely a question of convention and intelligibility.
But one thing I must confess: I would not for anything dispense with this compass on my psychological voyages of discovery.["A Psychological Theory of Types," CW 6, pars. 958f.]ß

Jung's basic model, including the relationship between the four functions, is a quaternity, as shown in the diagram. (Thinking is here arbitrarily placed at the top; any of the other functions might be placed there, according to which one a person most favors.)

Four Types

Jung believed that any one function by itself is not sufficient for ordering our experience of ourselves or the world around us; all four are required for a comprehensive understanding.

For complete orientation all four functions should contribute equally: thinking should facilitate cognition and judgment, feeling should tell us how and to what extent a thing is important or unimportant for us, sensation should convey concrete reality to us through seeing, hearing, tasting, etc., and intuition should enable us to divine the hidden possibilities in the background, since these too belong to the complete picture of a given situation.[Psychological Types," ibid., par. 900.] Jung acknowledged that the four orienting functions do not contain everything in the conscious psyche. Will power and memory, for instance, are not included, because although they may be affected by the way one functions typologically, they are not in themselves typological determinants.]

The ideal is to have conscious access to the function or functions appropriate for particular circumstances, but in practice the four functions are not equally at the disposal of consciousness. One is invariably more differentiated, called the superior or primary function. The function opposite to the primary function is called the fourth or inferior function.

The terms "superior" and "inferior" in this context do not imply value judgments. No function is any better than any of the others. The superior function is simply the most developed, the one a person is most likely to use; similarly, inferior does not mean pathological but merely less used compared to the favored function. Moreover, the constant influx of unconscious contents into consciousness is such that it is often difficult for oneself, let alone an outside observer, to tell which functions belong to the conscious personality and which to the unconscious.

Generally speaking, a judging observer [thinking or feeling type] will tend to seize on the conscious character, while a perceptive observer [sensation type or intuitive] will be more influenced by the unconscious character, since judgment is chiefly concerned with the conscious motivation of the psychic process, while perception registers the process itself.["General Description of the Types," ibid., par. 576.]

What happens to those functions that are not consciously brought into daily use and therefore not developed?

They remain in a more or less primitive and infantile state, often only half conscious, or even quite unconscious. The relatively undeveloped functions constitute a specific inferiority which is characteristic of each type and is an integral part of his total character. The one-sided emphasis on thinking is always accompanied by an inferiority of feeling, and differentiated sensation is injurious to intuition and vice versa.[A Psychological Theory of Types," ibid., par. 955.]

Jung described two of the four functions as rational (or judging) and two as irrational (or perceiving).
Thinking, as a function of logical discrimination, is rational. So is feeling, which as a way of evaluating our likes and dislikes can be quite as discriminating as thinking. Both are based on a reflective, linear process that coalesces into a particular judgment. Sensation and intuition are called irrational functions because they do not depend on logic. Each is a way of perceiving simply what is: sensation sees what is in the external world, intuition sees (or "picks up") what is in the inner world.

Besides the primary function, there is often a second, and sometimes a third, auxiliary function that exerts a co-determining influence on consciousness. This is always one whose nature, rational or irrational, is different from the primary function.

Four Functions

Jung's model of typology is the basis for modern type tests, such as the Myers-Briggs Type Indicator (MBTI) and the Singer-Loomis Personality Profile, used in organizational settings.