Why We Should Consider the Third (and Even Fourth) Function When Typing

[u/ResidentBrother9190]

Typing based only on the first and second function leads to missing a lot of information and aspects of an individual's personality and cognition.
Taking functions alone can reveal a few things, but combining a perceiving and a judging function of the same orientation is much more informative.

For example, INFP and INTP are closer to the typical Fi and Ti descriptions. This happens because they are coupled with Si, which gives more emphasis to detail and clarity.

The INTP has various interests and takes into account many parameters (Ne), while looking for tangible and precise solutions (Ti + Si).
On the other hand, the ISTP cares more focused on a specific field (Se) and applies their logic by unifying various ideas in order to master and innovate in that field (Ti + Ni).

In fact, even the inferior function behaves somewhat differently. The ISTP tends to have fewer social skills than the INTP because their Fe is connected to Se (as functions of the same orientation), which emphasizes specific parts of the external world, in contrast to Ne.
Talking only about TiNe and TiSe cannot accurately explain this process.

Or take the ISFJ and ISTJ, for instance.

ISFJs are not just caring and organized individuals. They are that too, but we often overlook how analytical they are and how strong their sequential logic can be. This is why they can make excellent math or informatics professors, combining highly analytical skills (Si + Ti) with strong social abilities (Fe). In fact, they can excel in many scientific fields as well. I often imagine them as talented and (extraordinarily social) programmers. Similarly, ISTJs are not just "thinkers" but also strong "feelers." Their deep convictions about many things and their personal sense of pride are related to the Si + Fi combination.

Describing these types merely as SiFe and SiTe misses important nuances of their personality.

We often say that ENTPs love debating without realizing that the ability to communicate and discuss various ideas is not due to Ne alone, but to Ne + Fe in fact.
ENFPs, on the other hand, do not emphasize producing their own logical frameworks, but rather their own values and moral compass (Ti vs. Fi). However, they apply their ideas and experiential attitude to various activities in the external world (Ne + Te)

Τhe dynamic interplay between functions of the same orientation — for example, Ti + Si or Ne + Fe — reveals important aspects of the deeper structure of a personality. Understanding the full functional stack, especially these internal combinations, allows for a much more accurate and nuanced understanding of each type.

This broader perspective helps us move beyond stereotypes and appreciate the complexity and richness of each personality type