Okay okay I will try to help. I am not a master at cognitive functions.. but I have an INFP brother and, maybe I can share little of my experience, which might help you.

My INFP brother:
He loves music.
He hates logic, science and logical world. He thinks as if "with only logic, this world has nothing meaningful left".
He doesn't exclude or reject logic, but he says that he rather appreciates creativity, he prefers creativity over logic.
And yes he feels his own feelings deeply.

So, and about your demon Ti story:
(Let me share a little portion of my story)

I am an INFJ , My enneagram is 3w4 . 3w4 means suppressing of emotions, while, INFJ means feeling others emotions too deeply.
And I had helicopter parents.
So you can imagine how I would have lived.
Continuous suppression of own emotions and being continuously feeling others emotions.

^ When I was 16, I had learnt some tactics from my dad and forcefuly socialized a lot in order to make friends and be "normal".
But few years later, I started feeling as if I am fake with myself as well.

Basically I had forced on myself ENTJ style!

Then I came across mbti and related so much to INTP.

I didn't even check INFJ's description. Because I was so convinced that I can't be a feeling type. Because my whole life I had been suppressing my emotions, even rationalising them!
And moreover my thought processes seemed to match to that of an INTP.
My head (enneagram ) is 7w6. Which seemed similar to Ne.
I am a 3w4, whose desires are similar to inferior fe. Being a 3w4 also means that I am constantly out of touch with my own feelings and authentic self.
Suppressing of emotions is something which INTPs do!
And also, I had a lot of Ti interests as well. I felt a lot of Ti inside me.

Basically, my enneagram was exactly opposite to my mbti type.

And,


Such kind of "demon Ti" stories arise, when you aren't emotionally healthy. Basically there might be some issues in your life. Address them. Maybe then you can know your type!


ALL THE BEST

 

You can argue it's demon Ti when you're using Ti to cut down "mean" people, but you are being mean or petty yourself. It counts as being mean/petty when you are trying to out-logic people just to have satisfaction at them losing an argument or being knocked down a peg.

For comparison, I think my demon Fi shows up when I'm suddenly feeling very emotional (usually in a negative way) and I use my emotional state to justify being selfish, lazy, or some other bad behavior. Since normally I don't notice or care about my emotional state, when I "feel my feelings" I easily convince myself that my feelings are right and I should express them. Other people express their feelings, so why not me??? I have the right, don't I??? This kind of mindset tricks me into going against my long-term principles in the short run.

 

The question is: what do I do now? I mean, Ti certainly isn't a problem in and of itself. But how do I know when it's the demon form and when it's something more benign? Any thoughts?

If Ti turns out to be a demon within you, find another who is fond if Ti and doesn't mind handling it. They could be your angel.

 

So this is really interesting because I as an INFP am very interested in philosophy science mathematics and logic and things but I often find my conclusions with logic to be disappointing and disheartening but nevertheless true, then I also have moments where im just out to prove things wrong (pluto is a planet dammit and if I need to come up with a way to divide by 0 or prove viruses as living organisms just to spite everyone who says otherwise I will), I also grew up in a household with an ENTJ Dad and ESTJ Sister so rather than use Te to actually keep up with their demands I think I resorted to Ti to poke holes in everything they told me as a way of protecting my own Fi but I definitely feel much more comfortable using Fi over Ti even if I do use Ti often enough. Long story short im in the same boat where I use it a lot but don’t know how to handle it properly and it just gets me in a rut of disillusionment

 

So Ti is a demon? I guess that makes me a demon, lol. INFP = Fi Ne Si Te. Yep. Ti is in the background. Here is my take on this. Fi is about personal feelings. Ti is about inner thinking. I like Ti and am supposed to lead with it, but Ti is not simple. It takes a lot of learning and background to do it well. Anyone can do it not so well. That is where an Fi person might get into trouble. But Fi is important. When things are not going well for me and my Ti, Fi I would expect to go upfront. Fi has to do with personal values and everyone has those.