Introverted Sensing (Si): The Inner Life of ISTJ & ISFJ Types

By Dr. A.J. Drenth

I’ve already written a fair amount about Introverted Sensing (Si), both on Personality Junkie and in my books. But having recently revisited Lenore Thomson’s book, Personality Type: An Owner’s Manual, I felt inspired to explore Si afresh via the lens of Thomson.

As you’re probably aware, Introverted Sensing (or what Jung called Introverted Sensation) serves as the dominant function for ISTJ and ISFJ types. Thomson asserts that, like Extraverted Sensing (Se), Si is “focused on data received through the senses.” Beyond that, however, Si and Se begin to part ways, for reasons we’ll now explore.

Immersing itself in external data procured by the five senses, Extraverted Sensing serves as the main tool of ESTP and ESFP types. Known for their cat-like reflexes and propensity to lose themselves in action, these types are highly attuned and responsive to external stimuli. Se doesn’t attempt to block or modify incoming sensations, but merely responds to them. This is why so many professional athletes and first responders are ESPs. Rather than overthinking things, as other types might be inclined to do, they develop and trust their Se instincts.

By contrast, when we look at ISTJ and ISFJ types, we see little, if any, instinct at play. Instead, what we find is a more deliberate, methodical, and predictable mode of functioning. Instead of spontaneously responding to the world, ISJs are guided by internalized rules, principles, and responsibilities. Let’s now take a closer look at the nature of Si and how it plays out in ISTJ and INFJ types.

Introverted Sensing (Si) in ISTJ & ISFJ Types

To kick things off, let’s examine another key passage from Thomson:

Ask five people who saw the same movie to describe what it was about, and it’s clear that each person is impressed by certain aspects of reality and not others. We don’t remember—or even notice—everything we see, hear… Only some things strike us as important, useful, familiar or exciting enough to convert into mental content—that is, into facts that we retain over time. Si guides this selection, and it prompts us to reconcile our new impressions with the ones we’ve already stored.

Here, Thomson highlights some important distinctions between Se and Si, some of which we’ve already touched on. One critical point is her use of the word selection, or what I might call discrimination. Namely, she is arguing that Si is more discriminating than Se in that it only pays attention to, or registers, sensations it deems salient or important.

But how does Introverted Sensing determine which sensations are important? According to Jung, all the introverted functions are rooted in subjective (read: inner) data. They use the self—its thoughts, feelings, perceptions, interests, needs, and desires—as a key reference point for understanding and navigating reality. Hence, at minimum, we can say that Si determines which sensations are worth noting and preserving by referencing the existing contents of the self.

Thomson also espouses that Si helps us “find ourselves” in whatever is happening, grounding our perceptions in what we already know. I don’t see this as necessarily limited to Si, however, as all the introverted functions are anchored in the self and tend to relate outer experiences back to inner ones. What we can say is that, like other introverts, ISJs tend to keep at least one eye on their inner world which they use as a lens and guide for the external world.

Thomson views Se as a “right-brained” function that “bypasses the left brain’s penchant for explaining things to itself” and engages with the external stimuli directly, that is, in a raw, unmediated way. By contrast, Si, as a “left-brained” function, feels compelled to collect information—names, dates, numbers, references, guidelines, etc.—that reflect, explicate, substantiate, or signify what it deems most important. I would add that ISJs also do so because the left brain assumes that there’s an “objective” or “right” way of doing things. This prompts ISJs to collect information from the sources they trust to guide and inform their decision-making. And once that information has reached the status of a belief, they can be reluctant to change their mind, even if scientists or other authorities are making claims to the contrary.

Further, Thomson suggests: “When Si is our dominant function, selective acquisition is our primary arbiter of meaning.” If we swap the term “acquisition” for the Myers-Briggs term, perceiving (remember, Si is a perceiving function), we could say that ISJs’ primary concern is selective perceiving. In short, they find meaning in amassing or recollecting information associated with their primary interests.

A good example of this is the beloved Los Angeles Dodger’s commentator Vin Scully—most certainly an ISJ type. Scully possessed an unsurpassed knowledge of baseball, particularly about his cherished Dodgers, including the personal histories of the players. His passion for the game, both its technical and personal aspects, shone through over his long and storied career. Not only did he enjoy learning about all things baseball, but also recollecting and communicating that information, for which he relied on his prolific Si recall.

Thomson goes on to highlight the role of Si as a stabilizing function. She suggests that we use Si to “stabilize our immediate sense impressions by integrating them with the ones we remember and care about.” In addition:

From an Si viewpoint, immediate conditions have no stable meaning. They’re just an influx of data impinging on the senses. And our response to these impressions depends on our mood, our state of mind, our desires, our feelings. It’s our commitments and priorities, the facts we hold inalienable, that give our circumstances enduring significance.

As discussed in our previous post on judger-perceiver differences, judgers expect (and generally desire) consistency over time. Thus, as Thomson rightly observes, they tend to keep the immediate situation at arm’s length, thereby reducing any stress or cognitive dissonance that might arise from changes in external circumstances. For ISJs, it’s preferable to fall back on, or associate things with, familiar beliefs or behaviors rather than engaging with the world anew. Of course, this is apt to be true of all introverts to some extent.

ISJs’ desire for stability, in combination with their penchant for selective perceiving, leads them to “acquire facts, objects, and a social role along the lines of their inner priorities” according to Thomson. As an example, she cites an ISJ who devoted all his spare time to finding and collecting old cylinder phonographs. She also declares ISJs the most likely of the introverted types to join clubs and associations devoted to their particular interests. Doing so helps reinforce ISJs’ sense of meaning, stability and self-worth.

Finally, Thomson rightly points out that, considering Si’s status as a perceiving function, ISJs are, on the whole, more experience-oriented than their ESJ counterparts, who lead with a judging function. Although ISJs and ESJs both use judging (Te or Fe) to deal with the outside world and thus appear quite measured and rational, their inner mode of being—their Si—is more open and experiential. Hence, ISJs are often quite leisurely in their spare time—doing arts and crafts, working crossword puzzles, putzing around at thrift shops, perusing funny quips and stories, etc. In this sense, they differ from ESJs, who are inclined to see free time as a chance to get more work done.

Learn More in Our Books:

My True Type: Clarifying Your Personality Type, Preferences & Functions

The 16 Personality Types: Profiles, Theory & Type Development

Related Posts:

Introverted Sensing (Si) | Extraverted Sensing (Se)

Type Profiles: ISTJ | ISFJ

The 8 Functions (Main Page)