Difference between ISTP and ISTJ.
I'm also simultaneously describing socionics ISTp and ISTj.
The functions between the systems ARE the same. If you analyze both systems, you'll realize that the MBTI articles are often inconsistent with the functional definitions. The articles are usually describing the manifestation of the functions of the other personality (J/P are switched).
Introverted sensing is a very aesthetic function, and the idea that it has to do with "rules" is bollocks, that's Te and Ti. Doesn't make any sense. A lot of stereotypes would portray ISFP's as big hippies who are very chill. Then we transfer over to ESFP and suddenly you get a very aggressive in your face and intense personality. Its inconsistent. ISFP's are often viewed as the most committed of SP's in relationships. Their primary function is a JUDGING function, and they often look very closed off to the world, up until they go to the club and start taking ecstasy and dancing their asses off and sleeping around with everyone they met that night... lol.
ISFJ's (MBTI) on the otherhand are very much the same flavor as ENTP. They can be quiet and stoic but have a very goofy sense of humor and barely take themselves seriously. They're usually quite lighthearted as well (unless they're E4, which is kinda rare in my experience).
ISTJ's are very aesthetically inclined and get frustrated over chaotic aesthetic elements. Loud noises, bad smells, etc. ISTP's are actually the rule makers and look very rigid in appearance. For example: celebok on youtube is an ISTP (many disagree because he's so rigid, but this is a manifestation of his primary Ti, a very order seeking function).
The only reason ISTP's are thought of as jocks or sporty is because of the ESTP's who think they're ISTP's... like myself, or the occasional ISTP athlete with more of a focus on Se than Ti. Those are the ones we're more used to.
Wrong.