Jo

Although it feels a bit silly at first to compare the two, considering how one is a perceiving functions and ti/fi are judging functions, there is still an overlap between the two, especially if you look at them from the outside. (Sensing/Intuition and Feeling/Thinking are two different categories that don't overlap with each other, hence also don't contradict each other. However, their behavior does overlap.)

In my opinion, a big issue on why those two (or any cognitive functions in general) can be confused is because people pay attention to the behavior on the surface rather than the thoughts and feelings behind said behavior.

This is an issue I see when it comes to typing in many typology systems, especially when it comes to enneagrams.

Yes, taking into account the behavior someone shows on the outside is a great indicator that will lead you to their type, but it's important to remember it shouldn't be the only criteria. Try to see what motivation could possibly be behind ONE action, and you can confirm if that motivation is true when another action happens in the future that affirms said motivation.

(Example: A friend talks about how they love being near nature. That can be a good indicator for extroverted sensing since se-users love connecting with the environment around them through their senses, but it can also be another function depending on WHY they love nature. Same friend some days later explains how nature is the only place where they can sit and ponder about life, the world, and overall understanding existence to a deeper level. Is that not a great hint towards introverted intuition? The complete opposite of extroverted sensing?)

The reason I brought up ni and fi/ti for this is because I personally find the overlap from those 3 very interesting. Maybe it's a bit biased considering how I was at a dilemma between all of the above for some long time. Maybe in the future, I'll talk about other functions and how they overlap. If I find the willpower.

Starting off with ni vs ti, maybe even harder to distinguish compared to ni vs fi since both ni and ti are detached from emotion, meanwhile fi is, well, literally all about emotions, values and your identity. Both ni and ti users may find themselves saying, "I know this is true, I just can't prove it."

-For Ni users, that's because their extroverted sensing picks up little clues around them and they subconsciously connect said data, leading to the truth which may show up like an "a-ha!" moment for high ni-users (dominant: INTJ, INFJ, auxilary: ENTJ, ENFJ)

-For ti users, due to the logical system that they have created internally to process information and knowledge, cutting clean said knowledge and categorizing it, analyzing it, they find themselves to quickly spot when something is "wrong", when something doesn't allign with their logical system, when something contradicts a knowledge that they have proven to themselves already. (dominant: INTP, ISTP, auxilary: ENTP, ESTP)

Here's the thing, one will know something is not true because they SEE the actual truth.

The other will know something is not true because it CANCELS OUT their already proven knowledge.

One can't prove how they know it because the process of collecting all the data and forming them into a big image happened subconsciously

The other, although ti users usually have valid arguments since it's a much more conscious function than ni, sometimes can't walk you through their logical reasoning for it is too personal and subjective. (That's why it's called INTROVERTED thinking)

Both ti and ni users are interested in the depth and layers of the world:

Ni can PERCEIVE the depths, look at the layers detached from any personal judging.

Ti can JUDGE the depths, using a personal yet logical approach to fitting the layers into their logical framework.

Ni knows WHEN something is true, ti knows WHY something is true.