Each personality type has four Cognitive Functions. Functions put language to the way they process information and make decisions, and their order is based on personal preferences. Thinking and Feeling are used to make decisions, while iNtuition and Sensing are used to process information. Each type is referred to by their top two functions. Internal functions are the ones you use in your head, and external functions are the ones you use to interact with the world around you.

The TeSi’s functions are:
1. Te – extroverted Thinking
Te is the primary way TeSi’s interact with the world around them. Te is all about effectiveness and getting things done. It is the TeSi’s primary decision-making process, which means that if a decision is needed in the moment, they will rely on what makes the most sense logically. They are primarily concerned with moving forward and are not interested in wasting time and energy nitpicking a solution to death before applying it. They make the best decision they can given the probabilities they're presented with. The most effective functional or workable solution is often obvious to them, and they are masters of maximization. Te can also make them quite competitive.

2. Si – introverted Sensing
TeSi’s naturally use Si to catalogue experiences and information they deem important. In particular, they remember their impressions of experiences they’ve had. They have an organized internal world and their mind can easily put similar pieces of information into appropriate categories. They learn straightforward, practical systems, rules, and strategies with ease and grace. Si gives the sense of the TeSi being grounded and can make them seem like they have a very linear, black and white way of thinking about things. (Though in reality they may see everything as shades of grey.)

3. Ne – extroverted iNtuition
Ne is the part of the TeSi that craves new experiences and ideas. For example, when coming up with an idea to execute a project, they can take a lot of details they’ve gathered from previous experience and put them together to form a really great concept. Ne can also fuel sudden “lightbulb” moments where an idea strikes them out of nowhere as they’re talking. It makes the TeSi likely to enjoy taking disparate things and thoughts and gluing them together to see what happens. It can also cause them to lapse into a sort of factual story-telling mode at any moment.

4. Fi – introverted Feeling
Fi is their last function. Fi helps them to assess situations to see how things match up to their values and beliefs. They may think of their Fi as their “gut instinct”. It helps them learn to be sensitive to the values and feelings of those around them. It can act as a warning system when they think a decision makes sense logically, but somewhere inside, Fi is the alarm saying it’s a bad idea. However, because Fi is the TeSi’s weakest function, they will often act with the swift decisiveness of Te first, before considering how their actions might affect the feelings of others or taking time to think about whether their decision lines up with their values. As the TeSi ages, they get much better at using their Fi towards the beginning of their decision-making process. Although the most effective option takes priority, they become more aware and careful about doing things that would hurt those around them.


Dominant Function and Core of the External World:

Extraverted Thinking
TeSi’s are constantly aware of their environment until they are honed in on an issue and get into problem-solving mode. They are very efficient problem-solvers, naturally seeing the best course of action for the best outcome. They are highly logical and are natural-born leaders, easily seeing what everyone should be doing to accomplish the task at hand.

While introverted Thinking (Ti) dominant people want to spend lots of time refining and perfecting their solutions, a healthy TeSi is confident in their in-the-moment problem-solving ability. They don’t need to spend lots of time refining and reevaluating things, because they know they can shift quickly and do spur-of-the-moment analysis if their ‘Plan A’ somehow falls through.

TeSi’s are often very driven individuals. They value autonomy and are the sort of person who is likely to get a job at 14-16 years old (as soon as they’re able). They work hard, and often make a name for themselves in whatever industry they’re in. They can be good at almost any type of work, but they commonly end up in sales, tech, law, or government. They are often C-level executives, managers, or entrepreneurs. While they may start at the bottom like everyone else, TeSi’s can be so driven and commanding that they are able to rise through the ranks with ease and grace if they put their mind to it.

TeSi’s are very goal-oriented and results-driven. You aren’t likely to see them continue with an inefficient method for long. It’s very obvious to a TeSi what is or isn’t going to work, and it can be frustrating when others don’t see solutions as obviously as they do. TeSi’s may be accused of being bossy at times, but when they’re healthy, they don’t bother correcting someone unless they value that person or their work. Although the “bossiness” of a TeSi can frustrate others, the truth is that those around them would be usually be lost without their leadership. 

TeSi’s thrive in systems of hierarchy, whether they are leading or taking instruction from those in charge (provided those in charge are competent and effective leaders). If no leader is apparent, the TeSi will usually step up to unite the group and see that things get done. They work most effectively when they know what boundaries and expectations they can operate within. When they are under a smart and effective leader who brings out and values their talents, they thrive. When they are under an ineffective leader, they will become very frustrated and will probably do everything they can to either have the leader replaced by someone competent, or do what they can to replace them in leadership themselves.

Although TeSi’s are very social people, they are not afraid of being disliked in most cases. They don’t shy from necessary confrontation and when it comes to interpersonal conflict, they are apt to want to resolve issues in a quick, efficient manner and then move on with life. Only when they feel someone has wronged them or wounded them very deeply will they feel the need to cut people out of their lives. In most instances, they prefer to resolve an issue and move on, without lingering too much in any emotional aspects of conflict. 

TeSi’s are very opinionated people, and are not shy about expressing their opinions in mixed company. They find debate stimulating and are won over by people who can hold their own in verbal sparring matches, as they don’t come across people like this often. If the other person becomes overly emotional with their arguments, or cannot articulate their points accurately and concisely, the TeSi will likely feel good in their "win" because they were able to keep their composure while explaining their side. They tend to get frustrated if someone does not understand where they’re coming from or tries to steamroll them with their own position without hearing the TeSi’s perspective.

TeSi’s like to play “by the book”. Any risks they take are likely to be very calculated, to the point that they probably aren’t very risky from the TeSi’s perspective because of their ability to conceptualize the logistics of the way their plans will work out. While they can be innovative, they are more likely to try new things within the context of an area they already have a level of knowledge and experience in. 

Second Function and the Core of the Internal World:

Introverted Sensing
Si is all about real-world experiences. TeSi’s, often without noticing, pay a fair amount of attention to how things that engage their 5 senses (seeing, hearing, tasting, seeing, smelling) affect them. They value their own experiences very highly, and typically have a very good memory or catalogue of details about them. They tend to remember their impressions of experiences rather than remembering the experiences themselves in exact detail and they use this information from the past to help them make effective decisions in the present.

Some examples could be a lawyer noting the particular elements that always need to be in place in order to convince the jury that someone is innocent, or a sales person noting the most effective strategies in their sales career over time so they can implement the best strategy in every situation.

Due to this high value for their impressions of real life experiences, TeSi’s feel very concrete internally. They are sure of themselves, their views, and their morals. They see the external world as a world of possibilities that can change at any moment, while they are internally very solid. They may seem stubborn and are not easily swayed.

People with strong Si naturally become pretty ritualistic in their everyday behavior because they find positive experiences that work for them and want to continue having those experiences. They also might highly value “traditions” in the personal sense. Perhaps they like doing the same thing on their birthday every year, or they have a special holiday tradition from their childhood that is very important to them in adulthood. However, Si is very subjective, which means each person who uses Si might value very different “traditions” or rituals.

Despite some popular stereotypes, TeSi’s do change their minds, though it might take longer for them than for other types. They often have a quirky, sarcastic sense of humour and they care deeply for those close to them, though they are far more likely to show their love in practical ways rather than being sappy and overly affectionate.

Because they can get an idea in their head and then become quite stubborn about it, TeSi’s might find themselves trying to do something they perceive as loving, only to feel like it’s thrown back in their face. For example, in an effort to be a good parent they may save up to finance their child’s college tuition for years, only to find have their child decide to be an artist and refuse to go to college. From the child’s perspective, it can seem like their TeSi parent is trying to push their ways of thinking and their values on the child simply because they think they’re always right, but they might miss the fact that their parent has been working very hard throughout their childhood to be able to provide them with an opportunity they believed would greatly enhance the child’s life in an effort to be a good parent.

TeSi’s might relate to the idea of their brain being like an internal filing cabinet that stores the information they gather from the world in an organized fashion. Once they learn the details of how a system works, they are unlikely to forget it quickly. They are easily able to map out the details of what needs to happen to make an idea a reality, as they have naturally linear thought patterns. Because they’re detail-oriented, they are often able to manage highly complex systems and highly detailed projects with incredible grace, whether it looks like managing all of the orders and customers for a business, or keeping track of all their kids’ activities for the week and finding a way to make sure everyone gets where they need to go. They may also use this to keep track of wealthy clients and their birthdays and family member’s names.

They tend to live knee-deep in the details which helps them manage high levels of complexity. It can be frustrating for a TeSi to see all the steps needed to complete a project, but others around them can’t see these details in the same way and execute them accordingly. This compounds  when the people they need to work with in order to accomplish their goals are oblivious to the work required. TeSi’s who understand that their mind works in a unique way and that others  have their own unique strengths will be able to plan better and accomplish more in a group setting.

People with strong Si like to know what to expect and to plan accordingly. Routine is one of the their best tools, and they wield it well. When they know what is expected of them, they can accomplish really great things. They are very reliable, and it’s hugely important to them that the people in their lives are dependable.

They can feel uncomfortable when faced with an entirely new situation where they have no past knowledge or experience to rely on. They greatly prefer having a set of criteria or a specific way to complete tasks that they know works for them. They are able to figure out the details as they go as long as they have similar experiences under their belt that they can piece together to form an understanding of the situation.

TeSi’s are generally very organized people. This is not to say they’re all perfectly tidy, but when it comes to something that matters, they plan, organize, and execute their plans in a very linear fashion. When they put their all into a project and have the right tools and resources, you can be sure it will be very well executed.

TeSi’s are great at seeing areas for improvement in people’s lives. Because highly detailed systems naturally make sense to them, they may see a problem someone is having and try to help the person implement their own system as a solution. When they’re younger, they might try to apply their solutions to any potentially relevant problem they come across, thinking, “If it works for the me, of course it should work for the person I’m helping!” As they gain more experience in life, they learn to recognize when their help is welcome and where their solutions are actually a good fit, and they become a lot more strategic about the way they help people.

TeSi’s tend to have very high standards for themselves, which can cause them to focus on where they feel they’re falling short, even though those around them rarely demand the near-perfection they demand of themselves. Because they can be very driven and often end up in leadership roles where they’re the pioneer, it can get exhausting if they’re in a role where most of what they hear is negative feedback. Being a leader causes all their flaws to become more visible, and the perception most people have of TeSi’s is that they have no feelings at all. This can cause employees and even family members to be unnecessarily harsh in the way they speak to and about TeSi’s.

Third Function and Supporting Role in the External World:

Extroverted iNtuition

Ne is the part of the TeSi that loves to explore abstract possibilities and is great at taking something—an idea, a person, etc.—and seeing beyond what it currently is to what it could possibly become. For them, well-developed Ne keeps Si in check so they don’t get too bogged down in the details. Their observations may be more “realistic” than someone with stronger Ne. This side of them is what causes them to see the world around them as a malleable, changeable thing.
For example, they might look at complex situation or problem and see all sorts of different logical solutions and outcomes, but they know it’s only possible if they take X, Y, and Z steps. This exploratory side of the TeSi tends to look on the bright side of things, while their Si perceptions keep them “grounded” in the concrete. They are very realistic people, neither overly pessimistic nor do they have their head in the clouds.

When a TeSi is explaining something, or theorizing about their ideas, they might be able to see the outcome they want for the conversation, but they might have trouble finding the right language to express themselves. The TeSi might repeat themselves several times with slightly varying vernacular, as they hone and refine their ideas. Through this process of verbal refinement and explanation, the TeSi might also come to realize new facets of their own point. 

It’s almost as if this process is like a download of information straight to their mouth—they are not necessarily aware of the new ideas being formed before they say them, and are fully realizing their point as they talk. TeSi’s can use this to their advantage when they have a problem. Talking it out with a trusted advisor or friend may help them realize new things about the situation which helps solve the issue. TeSi’s who haven’t fully developed their “filter” should be aware of their tendency to verbally process in this way and be careful with what they talk about and to whom. Writing their ideas down can help in a similar way as verbal processing to express their ideas, and may be a less vulnerable option to process more personal issues.

Their Ne may also come out when trying to make big life decisions, or solving major problems at work. They can see lots of good options available to them, but may feel that choosing just one means closing themselves off to all the other options. Because what they know they could potentially accomplish in their life is structured in a very linear way, they can see all the steps necessary to take before their dreams are realized, which may be overwhelming. They should be aware of this and make a conscious decision not to become paralyzed by all the options and the steps required to actually accomplish them.

Last Function and the Supporting Role of the Internal World:

Introverted Feeling
Introverted Feeling (Fi) is a slower decision-making process than their preferred Te method. Fi is the morals and values-based decision making process they use. Healthy TeSi’s typically operate by the “golden rule” of treating others how they would like to be treated. Because they put more emphasis on the the logical, blunt, take-charge side of themselves, they may view extremely soft-hearted people as being too sensitive.

For example, when someone reacts poorly to a great critique that they give because they know it could help that person improve immensely, they might think, “If I wasn’t being effective in that area and didn’t know it, I would want someone to point that out to me!” They might not know or take into account that others don’t operate like they do. Others may view the TeSi’s version of helpfulness as hurtful. 

They can unintentionally hurt people they care about in the moment while trying to help, but upon reflection they’re likely to realize that they hurt the person. It can take a few tries for the TeSi to know how to rectify such situations. Because their main method of operation is quick, decisive efficiency, they aren’t as inclined to ruminate at length over what should be done, or to spend a lot of time thinking through how their words and actions will affect others.

Fi is the small part of the TeSi that is quite vulnerable and sensitive. While others might view them as very blunt, outspoken people, inside they do have a soft heart. Their emotions, while perhaps uncomplicated, are felt very deep down. They don’t have very many emotional buttons, but when pushed, those they do have can bring them to their knees. Talking about their emotions - their innermost fears, their hopes, their love - may be quite difficult for the TeSi. 

If they are uncomfortable with this softer side of themselves, they will probably ignore it, which can lead to ruthless and cold behavior towards even those they care about. TeSi’s should be wary if they have a tendency to ignore their morality and emotions.

Their morals are decided without too much influence from others, although they will take their experiences with others into account. The more experience they have with a person, the more they are able to understand how to interact with them in an effective and caring manner. 

Ultimately, they value their own opinion the most. If they believe they are doing the right thing, they will be able to rationalize almost anything. This aspect of a TeSi’s personality can actually be a hidden strength. They can make advancements in areas that others might be afraid to venture into, because they aren’t worried about what others think of them. Their own interests and values can keep them going on the path towards their goal, even in the face of disapproval from those around them. TeSi’s aren’t likely to do something too far outside what their experience (or related experience of people they trust) has proved positive in the past.