Listen to them talk
INTJs talk about their thoughts / thought process (Te). They need to talk through or write down their thoughts to understand them fully. Notice how Sherlock constantly talks through his thoughts, and Hamlet is the king of soliloquies?
INTJs are usually going to be more direct and blunt in their communication, while INTPs are typically men/women of few words.
INTPs would rather think though everything in silence without the distraction of having to say them all out loud or explain them to anyone else. The worldview inside the INTP’s head usually remains a secret, not necessarily because they want it to, but because they just don’t see the point in vocalising their thoughts.
Both types can be equally logical, but they look at logic completely differently.
INTPs devise their own system of logic that doesn’t rely on facts and tends not to conform to the world’s sense of logic (Ti). They love to analyse things from all angles, whereas INTJs are more interested in using logic and information for how they can use it (Te).
An INTP and INTJ in an argument will both use logic, but oft times, the INTP will want to stop and define the terms, while the INTJ will want to simply come to a problem solution that they can use in real life. For the INTP, it’s all about the analysis itself, while the INTJ is looking at everything in terms of application.
This can, at times, make argumentation go south between INTxs. The INTJ will be frustrated because the INTP is interrupting the problem solving process to define the words used in an argument, while the INTP is going to be frustrated by the fact that the INTJ doesn’t see the point in doing so.
INTPs love to talk about their ideas (Ne). They get a certain thrill from having big ideas move through their mind, from analysing them. When they vocalise an idea, they’re not necessarily thinking about carrying it out
INTJs love ideas too, but their ideas tend to focus less on analysis and don’t exist purely for the ideas themselves as they do with many INTPs. Rather, the INTJ uses ideas to realise a specific long term vision (Ni).
INTJs don’t talk about their ideas so much as INTPs, so if you do hear them talk about a new idea, it means they’ve probably already decided to carry it out. INTPs on the other hand, are in it for the ideas, and will discuss all their ideas regardless of whether they’re going to do anything with those ideas later on. Te implements ideas, while Ti analyses them.
When it comes to INTJs, the only portion of their idea that you will actually see, is the finished product, their plan carried out. I’ll get an idea, and if I don’t see any way I could use it, I don’t bother analysing it. If I can use it, I implement it as soon as opportunity allows.
With INTPs, you’ll very likely see all the ideas, but only see half of them carried out (if even that much). My INTP dad is constantly talking about potential inventions, airplanes he’d like to build, lifestyles he’d like to have, but he’s so busy generating ideas that he doesn’t stop to think about how he’d accomplish any of them.
INTJs are reluctant to talk about their feelings and will prefer to work through hardship in silence. Other people typically have little affect on an INTJ’s feelings, they’re more in tune with their own feelings than other people’s.
INTPs ned to talk about their feelings –not as much as Fe auxiliaries or dominants, but they do need to let their feelings out. (Usually this is expressed as charisma for their ideas). INTPs are less in tune with their own emotions than they are with other people’s. They might not always recognise when they’re angry, but they’ll recognise when somebody else is angry.
When it comes to other people’s feelings INTJs don’t really empathise unless they have shared experience. At the same time, they also happen to be fairly good at figuring out people’s motivations using (NiSe).
INTPs are more likely to empathise with universal shared experiences than with individual emotions. If both an INTJ and an INTP were crying in a movie theatre, their reasons would be very different. The INTJ might cry because he had experienced the same thing as one of the characters in the film, while the INTP might cry because the he recognised suffering in another human being and had empathy for them.
INTJs won’t really talk much about the past, but will prefer to focus on the present (Se) and future (Ni).
INTPs will be more relate past experiences to the present (Si), not to the extent of upper Si users, but they definitely do have a sentimental side to them. In the INTP, this might show up as a desire to hold on to possessions given to them by their parents, or similar tendencies of that nature.
Experience of the Physical Environment
INTJs are more aware of their physical environment than INTPs. You move their stuff, they will know about it. INTJs notice details in their environment because they’re trying to…organise themselves within their environment (TeSe). They’re going to pay attention to little sensory details that other people miss, and as a result, too much can cause them to be overstimulated. They can often be hypersensitive to loud, sensory heavy places (Se). Thus the Twelfth Doctor’s sensory overload upon regeneration…
INTPs are not going to want to…organise themselves in their environment. An INTP is probably going to have a much messier desk than an INTJ, and they’re more likely to lose things around the house (TiSi).
INTPs tend to think of places in terms…not of what they look like, but what significance they have, or what memories they hold. Whenever my Dad and I go backpacking in all our favourite spots, I’m looking at it like a new place and he’s looking at it and remembering all the good memories he’s had there.
The INTJ will have lots of plans that it’s implementing, while the INTP will have lots of ideas that it’s moving past. I have an INTP friend that I go rock-climbing with from time to time and when we plan an outing, he will text me saying, “hey do you want to go climbing?” (Ne idea) and I will have to be the one to set up the plan “ok, what time?” (Te).
He’s really indecisive, so if I pick, I always like advanced notice (NiTe) and say, “how about this weekend.” If I make him pick, he’ll say, “how about in an hour?” (TiNe).
Then, even when we’re about to leave, he’s not always sure where we’re going, how long it will take us, or whether he brought everything we need because he crammed it all in the car last minute (TiNe). That’s how he likes it!
I on the other hand, keep a hiking rucksack packed and ready at all times under my bed so that I’m prepared to leave whenever necessary (NiTe). Even then, I still like advanced notice for everything. I still want to plan a hike a week in advance.
Dreams versus Future Reality
INTPs think of their future in terms of possibility and potential (Ne). They see a million different directions that their life could go and often have a hard time deciding which they want to follow (because they’re all so good!) (Ne).
INTJs view their future as a definite reality that just hasn’t happened yet and that they are responsible for making happen (Ni). INTJs usually figure out exactly what they want to be early on in life and make every decision with that end goal in mind (Ni) (example: David Tennant decided as a 3-yr-old that he wanted to play the Doctor).
In a way, INTJs feel they have a specific purpose in life that they’re meant to fill (Ni), whereas the INTP think of life in terms different ways their life could potentially develop (Ne).