A pretty good comparison and break down of the INFx types is this page:
INFP vs INFJ: 5 Surprising Differences To Tell Them Apart : Personality Hacker
I wrote up lengthy reply in the comments, which was mostly me being pedantic. Even though the author is ENTP, there is less pro INFJ bias than usual.
Oooh, this is a good description. I feel thoroughly validated by it!
Yes, that's an excellent portrait and corresponds well to the INFJs and INFPs I've known in my life.
The key to getting along with INFJs is demonstrating over and over again that you're a good and reliable friend who isn't about to hurt or take advantage of them. They are VERY perceptive about other people, BUT they also know that they tend to become blind w/r to those whom they love/trust too soon. Trusting someone, for them, means being able to relax those perceptions.
The key to getting along with INFPs is to realize that it's totally OK to disagree with them. It
feels like they want you to agree, based on the emotional tone of how they communicate, and that's what causes most miscommunication with them. The writer indicates that you need to "validate" their reasoning processes, but that doesn't mean validating their conclusions. Also, I don't think it means saying that their reasoning processes have no flaws. I think "validation" in this context means "respect" and/or "a lack of contempt". W/r to INTJs getting along with INFPs, this can often mean adding some verbiage to express that validation/respect, as INFPs don't seem to immediately read it from us. I.e., as with most people, they don't realize that
the fact that we INTJs are spending an extended period of time talking with them implies a great deal of respect.
(sighs). Drat, I thought I *had* it. Thanks as always for your patient corrections!
It's particularly useful for us INTJs to understand INFPs (and ISFPs), as they show us how our tertiary (and inferior, in the case of ISFPs) can be used in a positive, pro-active way. (It also helps to understand INFJs, but that doesn't require nearly so much work, as INFJs think so much like us that a lot of them think they're INTJs.)
The description of "Authenticity" (Fi) in that link is apt, and INTJs can hook into that. That same site has a good description of the INTJ:
The INTJ "Mastermind" Personality Type - Personality Hacker : Personality Hacker
A lot of INTJs I've shared this with believe it to be almost "too positive" a description. You can tell the author has a bias in favor of INTJs, but I think it's a bias based on intense sympathy and understanding and wanting to clarify where INTJs are often misunderstood. In terms of clarifying those misunderstandings, it's an excellent write up.
Check out this quote regarding Fi paired with Ni in INTJs:
However, their 10 Year Old process is Authenticity, a process which encourages them to be sympathetic of the subjective human experience. Whenever they engage in this mental process there’s a part of them that knows they’re a sitting duck… because they are. Perspectives allows them to see how others see, Authenticity encourages them to mirror back how others feel. Because an INTJ is able to occupy both the headspace and the heartspace of another person, they become at that person’s mercy.
This is one of those things that will have INTJs nodding and other types wondering, "WTF?! That doesn't describe the INTJs I know." This is in a section where she's about to describe how Te comes in to protect their vulnerabilities. Te harshness (or at least Ni-Te imperturbability) is what others see.
I quote this because it's a useful map for an INTJ to sorta-kinda understand INFPs (with the caveat that no one is capable of
completely understanding an INFP, not even other INFPs!), and it's also useful to understanding the INTJ growth areas. With this, plus having read how INFPs utilize "Authenticity", points to particular mental states that an INTJ can reach - mental states that we INTJs generally tend to avoid because they leave us vulnerable.
Understanding those mental states, and understanding their role in the overall pattern of INTJ processing, is remarkably helpful for INTJs. Imagine a world where
emotions make sense! Figuring out the "good version" of the "Ni-Fi loop" is quite helpful. I believe it looks a bit like this:
Tao Te Ching
...
As for the OP, I'm not a fan of Pierce's descriptions, overall. I like that he puts a lot of thought into them, but when he gets things wrong, he gets them really wrong. (This is where most MBTI descriptions benefit from being a bit vague.)