I adapted the following insights from Lenore Thompson’s Personality Type book. If you wish to learn more, I recommend it as an excellent, in-depth resource with far more insights than alluded to here.
Ti is a function that prompts ITPs to reason logically and impersonally with immediate data, by engaging situations in the here and how and adjusting to them in light of their impact on the goal. It operates by allowing the ITP to reason experimentally rather than analytically. It allows someone to work something out by doing it. With its all at once approach to life, Ti does not require exact predictability before it takes action. It makes decisions based on probability and leaves room for the unexpected and random. It recognizes, mid-action, which variables are best taken into account and which are relevant to the desired outcome.
When Ti and Se mix, it feels more like “instinct” to them than “being rational.” They do things “in the zone.” When combined with Ne, NTPs have a strong interest in patterns and their structural relationship to the immediate context. Ti is difficult to see in combination with Se, because the focus lies on what is happening as a result of Ti—seeing the adjustments made by the ISTP. STPs believe they are using their reflexes, when they are actually using their reasoning. Ti for them directly translates into physical adjustments.
ETPs use Ti to exploit a situation’s potential for excitement and to “compete” wherever they happen to be. Ti for the ITP is much more personal. The logic of the situation guides their direct experience. They need to be part of a process—the dialogue between a situation’s structural potential and its material realization. Ti understands reality only in terms of their ability to “converse” with it, and take part in its “becoming.” ITPs understand what it means to be in harmony with a situation still in flux. The level of their involvement makes them a “part of the process,” changing its nature by changing themselves. ITPs will sacrifice objective considerations for the sake of a project or experience that “feels right” to them. This may look impulsive or even be destructive, but their decision-making is subjective.
ITPs do not fully recognize their responsibilities to others unless they cultivate Fe. Prior to this, they will be naïve and careless in relationships. They know more about where they don’t want to be than their intended destination and simply refuse to do whatever does not appeal to them. They feel little need to consider others’ interests in the matter. Unless the ITP can have a direct impact on an unfolding situation and its logical outcome, they don’t know how to relate to it, especially if it involves an emotionally intense situation (such as the hospitalization of a loved one, and waiting for news). When they do engage with a situation or individual, they are unfailingly generous and almost without boundaries.
ITPs brandish their auxiliary function like a weapon to control the situation and protect Ti. They try to bar others from having an influence on them or avoid situations with no control over their environment. Unlike ETPs who leap into whatever turns up, ITPs know exactly what they excel at and stick to it. Using familiar skills, for them, makes every situation unique, random, and exciting. They divide all their attention between a few areas of technical or physical expertise.
ITPs use their tertiary function defensively and suspiciously. INTPs may focus on their material well-being and become convinced some foods are bad for them. ISTPs may see shams and hypocrisy wherever they look. Both can become conspiracy theorists, and it can be impossible to convince them these conclusions are illogical.
Due to the strength and persistence of Ti, ITPs tend to stick to what they know because its meaning is clear to them and under their control. They find a niche in a specific area of technical expertise. This keeps them locked into dominant Ti.
Fe in the INTP is usually egocentric and primitive, seeking attention and approval. ITPs tend to reject Fe development, trying to become emotionally unavailable to self-protect, but this only results in them feeling more vulnerable. Underdeveloped ITPs are indifferent and may even appear to others to lack a moral conscience, due to paying so little attention to others’ reactions to their statements or behaviors. Their indifference to others can turn to over-focus (seeking excessive flattery, approval, and attention). Paranoia that others are trying to humiliate them can lead the ITP to make arguments public. ISTPs may react in a direct, physical manner, but INTPs worry over their professional reputation and may defend their thoughts in a scholarly manner (through scientific journals or letters to the editor).
Without Fe development, ITPs are nearly oblivious to social rules and the nuances of relationships. They may turn them into a strategic “game” instead of emotional investment in them. ITPs must learn self-awareness from an outside perspective in order to see themselves as others do and become aware of their impact on people. Fe development leads the ITP to feel responsible to any situation they are n and recognize the power and influence of ordinary human decency. They realize their actions and words hold uncalculated meaning for others and link them to the larger community, whether they admit it or not.
ISTPs and INTPs appear on the surface to have little in common. INTPs are fascinated by the internal architecture of systems—the fluid relationship between form and context that determines a living process. INTPs want to get at a pattern’s essential nature by making many models of it. In many ways, this unfolding dance of variables between a design and its surrounding conditions is more important to them than the practicality of the objects they create.
ISTPs know the same symbiotic relationship between their intentions and the underlining structure of a situation. ISTPs are entirely present-oriented, tied perceptually to their context. The nature of their logic is experimental. ISTP depend on first-hand experience for what they know and cannot relate to situations where they can’t use their body-based logic. ISTPs may consider their tools as extensions of themselves, part of their bodies, capable of expressing what they cannot (like a musician’s guitar being a ‘third arm’).
Traditional methods of education or frameworks bore the ISTP, who excel in jobs that allow them to formulate tactical parameters based on real situations and people. ISTPs must be active to use their logic, which is tied to their direct experience. Hands-on involvement tells them a situation’s impact and the affect they can have on it. Without this external focus, they are bored and restless. They reason with their bodies as a situation is happening. Their Ti grasps what is possible in the moment. ISTPs usually learn things by touch, ear, or instinct, so they can grasp the underlining structure of whatever they are interested in. Their skill is to be fully present in whatever they are doing. They always want direct, hands-on involvement and the freedom to improvise.
Unlike ESTPs, ITPs do not require novelty to stay interested and are not indiscriminate. They may spend hours perfecting the same Ti skills; every day the experience is completely different for them. Many ISTPs narrow their world into niche interests and may be oblivious to what is happening outside it. Because they work with the logical implications of a system, and not in hierarchical terms, they can usually manage others professionally without making them feel like subordinates.
Because of their passionate sensory interests, ISTPs may appear more in touch with their emotions than is the truth. They use Fe only in accordance with Ti, and their ability to sort out and understand their own emotions is poor. Since encouragement has little impact on them, neither will they freely offer it. ISTPs may lose interest in others when they change direction. Extreme ISTPs, too dependent on Ti without enough extroverted functional development, may be angry over how others appear to want to control them or force them into socially appropriate behaviors. They may believe others who lack their background and experience have no right to demand anything from them or to judge them. They may dwell on feeling disrespected and develop suspicions toward society on the whole.
ISTPs must learn to adapt in order to gain the experience they need to feel included, and to learn that they cannot ignore human needs, either their own or of other people. They will learn this once they realize that logic dictates that they align with basic generous human behaviors, which will help them succeed and maintain positive relationships.
INTPs care about the logical possibilities of a structure—how form and context change and interact with each other. They are more at home with theoretical reasoning than the ISTP. Their model of engagement with a system is through design and model-making, in order to understand its inner framework. (Design, blueprints, etc.) They are often more interested in an idea that animates a system and its impact on reality than its objective usefulness (consider the theory of evolution as an example; a theory that encompasses the system of outward reality—life itself). They strive for theoretical systems that include all possible variables. Due to the complex inner entanglement of their thoughts, they may resort to broad metaphors in an attempt to get across their abstract concepts.
ENTPs see the potential of a situation first and then work out the structural design for making it happen. INTPs work the other way around. They recognize the structural pattern first and then look for how it impacts what already exists.
INTPs find it hard to know what they are feeling until they are out of control. They can be shy and awkward about emotional connections. The personal realm (such as in the shape of emotional connections and human relationships) appears to them to be without rational order—wholly illogical. Extreme INTPs, without extroverted functional development, can be excessively argumentative and defensive of their ideas, spending great amounts of time and energy defending their thoughts on public forums, in newspaper articles, and other forms of writing.
INTPs use their Ne to assess logical probabilities in systems. They must make an effort to apply that model to themselves, to see their impact on others or to entertain possibilities outside their limited, familiar framework of expectation. Without Fe development, INTPs see their problems as caused by other people, not as a product of their own shortcomings. They may respond either by seeking excessive approval from their peers or by seeking to increase their self-reliance, and refusing to accommodate, tolerate, or listen to others. They may also struggle with low Si problems. Well-developed Si recognizes information with consistent and useful meaning to the person who has it; INTPs may instead use it to ignore social conventions and expectations, detach from reality, worry over their physical health and well-meaning, or become hypochondriacs.
INTPs confuse their ability to be impersonal with the ability to be objective. INTPs who embrace extroverted functional development have a strong sense of purpose but do not feel the need to calculate their behaviors in terms of logical probability alone.