One of the things that makes Myers-Briggs® theory so nuanced and, I think, useful in certain settings is the function stacks it describes. This is also one of the more complicated aspects of this typology system. I’ve spent quite a bit of time since I first became interested in Myers-Briggs® personality types trying to understand function stacks and how to explain them to others. I think I did pretty well at that last one in “The Simplest Guide to Myers-Briggs® Functions Ever,” but it’s still not entirely complete.

I recently had a commenter ask for more information about how functions work for introverts, and that made me think that it might be useful to have a whole post on this topic. If you’re not all that familiar with functions (also called mental “processes”), then you’ll probably want to start with my Guide to Myers-Briggs® Functions. To briefly recap that post, if you’re looking at the letters for a person’s type, Sensing and Intuition are both Perceiving functions (or “learning processes”). Feeling and Thinking are both Judging functions (or “decision-making processes”). If someone is a P-type, then that means their Perceiving Function is extroverted. If someone is a J-type, then that means their Judging function (either F or T) is extroverted.

A Few Examples

Talking about how extroverted and introverted cognitive functions are determined by the J/P preference is enough to make your eyes glaze over, even if you know what’s going on there. Looking at some examples makes this idea much easier to see:

• For an xNFP type, the “P” tells us their perceiving function (in this case N) is extroverted. Therefore, both INFPs and INFPs use Extroverted Intuition and Introverted Feeling (since whichever of the two middle letters is not extroverted is introverted).
• The same thing happens for an xSTP type—their perceiving function (S) is extroverted and their judging function (T) is introverted. Both ISTPs an ESTPs use Extroverted Sensing and Introverted Thinking.
• For an xSFJ type, the “J” tells us their judging function (in this case S) is extroverted. That means their perceiving (F) function is the introverted one. Therefore, both ISFJs and ESFJs use Extroverted Feeling and Introverted Sensing.
• Similarly, an xNTJ type would use Extroverted Thinking and Introverted Intuition because their judging function (T) is extroverted and their perceiving function (N) is introverted.

Basically, the S or N preference tells us which Perceiving/Learning function a person uses most comfortably. The T or F preference tells us which Judging/Decision-making process someone prefers to use. And the J or P preference tells us which of those two functions (S/N or T/F) is extroverted. Once we know of of someone’s two favorite functions is extroverted, then we know the other one is introverted.

How an Introvert’s Functions Work

With that background, we can bring the Introvert/Extrovert preference into this discussion. The letter E or I in a personality type tells us which of those two functions is someone’s dominant function or “driver” process. Introverts, they prefer the introverted function (e.g. an ISFP prefers Introverted Feeling over their co-pilot Extroverted Sensing). Their dominant function is whichever of those first two functions is introverted. To return to the four types we looked at in the previous section:

• an INFP leads with Introverted Feeling and an ISTP with Introverted Thinking (their Judging functions)
• an ISFJ leads with Introverted Sensing and an INTJ with Introverted Intuition (their Perceiving functions)

The thing that makes an introvert’s function stack a little strange is that their dominant function does not match their J/P preference. Even though an INFP has “P” in their four-letter type, their favorite function is actually their judging function, Introverted Feeling. Similarly, even though an INTJ has “J” in their name, their favorite function is their perceiving Introverted Intuition.

In summary, the J/P preference tells us which function is extroverted, not which function is dominant. The E/I preference is what tells us which of a person’s top two functions is dominant.

What This Means For Introverts

So what does all this technical stuff mean, practically, for introverts? For one, if you’re taking a free online test inspired by Myers-Briggs® that there’s a good chance it won’t get your J/P preference right because many of those tests try to treat Judging-Perceiving as a dichotomy rather than as an indication of which cognitive function you prefer. A test that’s based on cognitive functions, like this one from Personality Hacker*, will give you a much better idea of what your best-fit type is.

• *please note that the link to this test is an affiliate link. You won’t be charged to take the test, but if you choose to buy any of their products after taking it I’ll receive a commission at no extra cost to you.

The fact that an Introvert’s preferred function is concerned with the inner world also means that most of us have to use our co-pilot extroverted function quite a bit in order to function effectively in the outer world. The introverts who become pretty comfortable with this function might be mistaken for extroverts (just like extroverts who spend time developing their introverted side might be mistaken for introverts). Even introverts who know they are introverted are typically forced to spend time using their extroverted co-pilot because we use it to interact with other people and either learn new information (if we’re a P type) or make decisions (if we’re a J type).

An introvert’s function stack can also play a role in their personal growth. From what I’ve seen, this tends to happen one of two ways:

1. an introvert will shy away from using their extroverted co-pilot process and instead spend time developing their dominant introverted function and their tertiary function (which is also introverted). That means working on their co-pilot process will be one of the best things they can focus on for personal growth (this is what Personality Hacker says is the case for most people).
2. an introvert will be forced (or choose) to use their Extroverted co-pilot more than their dominant introverted function. That means getting comfortable with their introverted side and working to balance it with their extroverted function is one of the best things they can focus on for personal growth.

One of the things that I like about Myers-Briggs ® types is that it gives you a description of the strongest mental processes that you have at your disposal. If you’ve settled on INFJ as your best-fit type (for example), then that can help you figure out where your strengths and weaknesses are. It can also give you an idea where to focus on for personal growth. For example, if an INFJ wants to strengthen their ability to make decisions, then it’d help to focus on developing their Extroverted Feeling side. If they wanted to strengthen their ability to see things from other perspectives and make logical sense of incoming information, then they’d want to focus on balancing their introspective Intuitive and Thinking sides.

Has learning about function stacks (here and from other sources) helped you understand and use Myers-Briggs® types? What are your favorite examples or analogies to use when explaining function stacks to other people?

If you’d like to know more about function stacks and how they work for the INFJ personality type, check out my book The INFJ Handbook. I’ve updated this second edition with a ton of new information and resources. You can purchase it in ebook, paperback, or hardcover by clicking this link.

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