By Dr. A.J. Drenth

Thought to comprise over 10% of the general population, “ISTJ” is among the most commonly encountered personality types, outnumbering the INTJ at a clip of ten to one.

ISTJs are among the most loyal, dutiful, and responsible of the types. They make loyal friends and companions and are admired for their devotion, steadfastness, and perseverance. If ESPs are the hares of the sixteen types, ISTJs are the tortoises. They work slowly and steadily until the job is done, fastidiously attending to all the details along the way.

In order to understand ISTJs, one must first understand their dominant function, Introverted Sensing (Si) , which compels them to preserve and protect past ways of doing things. Their Si characteristics led David Keirsey to rightly describe them as “guardians.” ISTJs guard and defend traditions and conventions, particularly those they have significant personal experience and familiarity with (e.g., their childhood religion).

Like the ISFJ, ISTJs can grow attached to the routine and familiar. The more often they do something in a particular way, the harder it is for them to break out of that pattern. This not only applies to their behavioral habits, but also to their beliefs and worldview, as many ISTJs continue in the same belief system in which they were raised.

While ISTJs are at times viewed as stubborn or finicky, they are actually more easygoing than is typically accredited them. Since Si is a Perceiving function, their first preference is to assume a receptive rather than controlling attitude. Unfortunately, this often goes unnoticed, since Si is introverted in direction. This is especially true in work settings, where ISTJs are more apt to call on their auxiliary Te. Once away from the workplace, however, most ISTJs know how to be leisurely, something the ESTJ can have a harder time with. In short, ISTJs are far less rigid and controlling (especially inwardly) than they are sometimes painted to be.

In sharing the same dominant and inferior functions, ISTJs have much in common with ISFJs. However, their auxiliary functions do confer significant differences. ISFJs use Extraverted Feeling (Fe) as their auxiliary function, which grants them a greater measure of social and emotional intelligence. And while ISTJs may lack some measure of social grace, their auxiliary Thinking function (Te) contributes stronger powers of logic and tactical intelligence.

Although differing in only one preference (i.e., J-P), ISTJs actually share zero functions with ISTPs. ISTPs, who use Se instead of Si, are less concerned with past precedent than ISTJs are. Their Se also confers a stronger desire for sensory and material novelty. Lastly, ISTPs are more inclined toward “hands-on” work, whereas ISTJ career-seekers are more disposed to administrative or other “white collar” sorts of work.

ISTJ Personality Development & “Functional Stack”

Each personality type prefers to use four of the eight functions first described by Jung. These four functions comprise a type’s “functional stack.” The relative strength of preference for these four functions is expressed in the following manner: dominant, auxiliary, tertiary, and inferior. ISTJs’ first preference is Si, followed by Te, Fi and Ne respectively. This is depicted in the arrangement of their functional stack:

ISTJ Functional Stack Dominant: Introverted Sensing (Si) Auxiliary: Extraverted Thinking (Te) Tertiary: Introverted Feeling (Fi) Inferior: Extraverted Intuition (Ne)

While we will soon discuss each function in greater depth, for now, we will turn to another feature of ISTJs’ personality—their type development. As is true for all types, ISTJs’ type development consists of three general phases. These phases roughly correspond to the ordering of the functional stack, with Si being the first function to blossom, Te the second, on so on. But as we will see, the inferior function is sort of a special case, summoning ISTJs’ attention at an earlier phase than might otherwise be expected.

Phase I (Childhood-20s)

Phase I is characterized by the development and rise to power of their dominant function, Introverted Sensing (Si). ISTJs use their Si to absorb, integrate, and reflect on acquired information and personal experiences. Phase I ISTJs may also show some development of their auxiliary function, Extraverted Thinking (Te), which can serve as a helpful extraverted tool for navigating and managing the outside world.

Phase II (20s-30s)

While the inferior function is not entirely dormant or inert in Phase I, the epic tug-of-war between the dominant and inferior does not come to the fore until Phase II. Once ISTJs’ dominant Si reaches a certain threshold of strength and dominance, their inferior function, Extraverted Intuition (Ne), begins to assert itself and play a more prominent role. This can be somewhat confusing since Ne is not next in line in ISTJs’ functional stack, but can be understood as deriving from its bipolar relationship with their dominant Si. Phase II ISTJs also show increasing use and development of their Te and may even begin to tap into their tertiary function, Introverted Feeling (Fi).

Phase III (30s, 40s, & Beyond)

If all goes well and they are fortunate enough to enter Phase III, ISTJs become increasingly aware of the insidious ways of their inferior Ne. As they become more aware of their inferior and learn to function more healthily as ISTJs, they experience greater balance between their Si and Ne, as well as an increasing sense of peace and wholeness.

ISTJs’ Dominant Function: Introverted Sensing (Si)

ISTJs use Introverted Sensing (Si) as their dominant function. Si types (i.e., SJs) are quite different from Se types (i.e., SPs). Unlike SPs, ISTJs are not sensation-seekers. They do not venture out seeking novel sensations, experiences, or material goods. They typically prefer a more routine, careful (versus carefree), and predictable lifestyle.

Si undergirds ISTJs’ propensity to function as conservators of tradition. However, because Si is a Perceiving function, ISTJs are less inclined to function as frontline activists for their beliefs or values than ESJs are. Rather, ISTJs prefer spending time reflecting on the past and their cherished traditions. Many enjoy attending religious services or studying religious texts, activities that support and strengthen their Si convictions.

Another feature of Si is its role in bodily sensation. Namely, it serves to monitor internal bodily affairs, ensuring that bodily needs are satisfied. As an introverted function, Si is more intensive than Se is, which can make ISTJs more sensitive to certain sensory stimuli. They may be hypersensitive to things like lighting, room temperature, noise levels, etc. This can make them more irritable than other types when sleep-deprived, hungry, or otherwise physically uncomfortable. Sensitivity to strong or unusual flavors and textures may lead them to adopt a relatively bland or routine diet.

We can also compare Si with its intuitive cousin, Ni. As Perceiving functions, both can be viewed as functioning rather passively. Both can also be associated with strength of conviction, as SJs and NJs alike can seem outwardly stubborn, opinionated, or closed-minded. The chief difference between these two functions is that Ni is a synthesizing function, weaving together disparate information to construct its own impressions or interpretations. Si, by contrast, does not see a different reality behind immediate sense data. Instead, it compares present experiences to past ones. For Ni, every experience is new and interpreted on its own terms. For Si, the past plays a more prominent role in interpreting the present.

While it can be easy for other types to criticize ISTJs for their conservative ways, we should not overlook their value and purpose. ISTJs remind us of where we’ve been and can thereby keep us from repeating our past mistakes. Their Si also serves as a necessary cultural counterbalance to Se, reminding us that material resources are limited and should be handled with care and concern.

ISTJs’ Auxiliary Function: Extraverted Thinking (Te)

Extraverted Thinking (Te) serves as ISTJs’ auxiliary function. It undergirds their tendency to outwardly express their judgments and opinions. ISTJs’ tendency to “think out loud,” by way of their Te, can be both a strength and a weakness.

On the one hand, their Te can make ISTJs strong and effective teachers or managers. On the other hand, it can result in them coming across as brusque, dogmatic, or controlling. Like other Judging types, ISTJs can be prone to overstating things or saying things that, in retrospect, they wish they could rescind or at least soften.

Unlike Extraverted Feeling, Te is not oriented to the preservation of social harmony. It is less personal and less attuned to others’ feelings. ISTJs’ preference for Te may therefore lead others to perceive them as lacking some degree of tact or empathy.

Te also strives to bring order, control, and rationality to external systems and operations. The modern world, characterized by a snowballing of bureaucracy and “red tape,” might be viewed as an offspring of an unchecked Te. ISTJs’ Te, in combination with their Si, makes them well-suited for administrative, clerical, and other careers that require careful attention to detail, protocols, and procedures. While other types may find highly structured work settings off-putting, ISTJs find them comforting, since they know what to expect and what their role is according to the delineated structure.

ISTJs’ Tertiary Function: Introverted Feeling (Fi)

Introverted Feeling (Fi) is ISTJs’ tertiary function. As an introverted function, Fi involves an inner focus on and analysis of personal feelings and values. Of all types, IFPs, who use Fi as their dominant function, are literally the most “self-focused” (in a neutral sense) with respect to their concern for independently exploring and managing their values and emotions. ISTJs, by contrast, whose Fi is far less conscious, do not always enjoy ready access to their own emotions.

As an inner Judging function, Fi grants IFPs a strong sense of inner self-control. But since ISTJs’ Fi is in the tertiary position, they do not enjoy the same degree of inner control. To compensate, they, like other TJ types, focus more on shaping or controlling the outside world via their Te.

One of the more important features of Fi is its direction. Namely, because it is introverted, onlookers are often barred from accessing ISTJs’ emotions. This is exacerbated by the fact that Fi is subordinated to Te in their functional stack. Consequently, can sometimes appear cold, aloof, or otherwise unemotional.

As ISTJs tap into their Fi, they begin to attend more closely to their personal feelings and values, as well as those of others. They begin to recognize and appreciate the merit of subjective concerns, acknowledging that truth or value is not limited to past precedent (Si) or external standards (Te), but can also include individual preferences (Fi). In opening to their Fi, ISTJs can become more compassionate and understanding, even toward those at the other end of the political or religious spectrum.

ISTJs’ Inferior Function: Extraverted Intuition (Ne)

As is true of other types, ISTJs can be blinded to the degree to which their inferior function impacts their decisions and behavior. Without sufficient awareness and integration of their inferior, ISTJs will be prone to unwise decision-making. Consequently, ISTJs seeking personal growth must work to understand the ways their inferior function, Extraverted Intuition (Ne), manifests in their personality.

Ne is concerned with generating and connecting ideas, as well as seeing all the various options and possibilities. Prone to seeing connections and associations everywhere, it is an unpredictable and highly divergent function. This is why Ne types are often viewed as quirky and unconventional creatives. While it is true that ISTJs are rather routine and conservative in their ways, there are numerous ways in which Ne can manifest in their personality.

One way ISTJs may indulge their Ne is through various sorts of speculation or prognostication. One of the most common ways ISTJs do this is through gossip. By proffering theories about various people or happenings, they secure an ego boost for their Ne. They also enjoy propagating various religious or political theories.

ISTJs also engage their Ne in their hobbies, such as word or math games. I know a number of ISTJs who enjoy working crosswords, Sudokus, or other sorts of puzzles. Such activities allow them to exercise their Si recall, utilize Te strategies, and make associations and experiment with possibilities (Ne). Many ISTJs also enjoy a variety of arts and crafts that allow for creative use of their Ne.

ISTJs also employ their Ne is by looking for creative ways to teach others. In addition to their desire to impart Si-Te information, creative use of their Ne may be another reason ISTJs gravitate toward teaching.

As for other types, integration for ISTJs does not occur through direct use or development of their inferior function. Rather, ISTJs are better off allowing their Ne to remain unconscious, functioning passively in the background. Instead of trying to develop or display more foresight, cleverness, or creativity, integrating ISTJs do what ISTJs do best, focusing their time and energy on Si and Te, while trusting that, in due time, everything else will fall into place.

For a more extensive look at each of the ISTJ’s personality preferences and functions, be sure to explore our latest eBook, My True Type: Clarifying Your Personality Type, Preferences & Functions.

Related Posts:

ISTJ Careers, Jobs, & Majors

Extraverted & Introverted Intuition as Inferior Functions

Famous / Celebrity ISTJs:

Jeb Bush, George H.W. Bush, David Hume

Note: This ISTJ profile may also resonate with Enneagram Sixes (6w5) and Ones (1w9, 1w2).