A conversation that doesn’t run out
Both types are introverted and intuitive, so they take in the world through patterns and symbols more than through detail. A question like “why do people stay in jobs they hate?” can start at dinner and still be going at midnight. The INFJ brings insight into motives; the INTP brings a talent for testing whether the explanation holds up. Each pushes the other’s thinking further than it would go alone.
They also tend to respect each other’s solitude without needing it explained. An evening in separate rooms, reading, doesn’t worry either of them.
When the theory is about a friend
The INFJ comes home upset because a close friend just ended a long relationship, and starts working out why it happened. The INTP, interested, begins questioning the theory: is that really the cause, what about the timeline, couldn’t it be something else? To the INTP this is engagement. To the INFJ, who wanted company in feeling sad, it lands as being argued with.
Plans are the other rub. The INFJ likes to know by Wednesday what Saturday holds. The INTP prefers to keep Saturday open in case something better turns up, and may still be undecided Friday night. The INFJ reads that as low priority; the INTP reads the INFJ’s question as pressure.
Practical ways to meet in the middle
Ask what kind of conversation is happening. A quick “are we solving this or sitting with it?” tells the INTP whether to bring the logic out yet. The INTP can also say, before debating, “I’m testing the idea, not you.” That small label takes the sting out of a lot of questions.
On plans, try a split: the INFJ fixes one firm thing each weekend and the INTP keeps the rest loose. For feelings, the INTP may need a day to know how they feel; agreeing that “I’ll tell you tomorrow” counts as an answer stops the INFJ from filling the silence with worst cases.