Since this topic continues to pop up, and most people seem tired of trying to describe, I've decided to make a post about it to be able to get my point across in one clear, logical format: stop switching the J and P!
1. It's a myth that the J and P are supposed to switch.
Original Socionic types in Russia were labeled with acronyms such as SLI, EIE, etc... not the four letter acronym. The four letter is the MBTI acronym, and the goal of converting the Socionic types into the MBTI acronym was to make them more usable and compatable (for us in the West). They (people like Segei Ganin from socionics.com) labeled the SLI as an ISTp, the EIE as an ENFj, etc... because they were supposed to line up to the MBTI type. They were the most compatible. If the SLI was the same thing as the MBTI ISTJ, then the Socionists would have called the SLI an ISTj, not an ISTp.
Also, keep in mind that the definitions for the Judging/Perceiving scales are pretty much the same thing.
So, why are the functions different?
2. The two systems define the functions differently.
They both define the functions in ways to fit their systems. If you read through the functional description on different MBTI and Socionic sites, you'll see the differences. In MBTI, your outer world determines your J/P, whereas in Socionics, it’s your dominant function. Socionists claim that if your base function is a perceiving one, then you are a perceiver, and if your base function is a judging one, then you are a judger. In MBTI, if you have Se or Ne then you are a perceiver… always, no matter if it is you base or secondary function.
3. The differences between the definitions of the functions in the systems.
One example is the function Ti. Socionics defines Ti as structural, or systematic logic. It’s about those things, logical systems, laws, and rules, and also analytical thought (when it’s the dominant function). Ti closes itself off from the outside world of facts and production to be able to manipulate them into this logical structure that they have in their heads, conscientiously seeing that system; looking through it.
Te in Socionics is a little bit different. I like to think of it as “logical juxtaposition”, other words thrown around to describe it have been “positivism”, “producing”, “practical”, “concrete logic”, etc… Te takes what happens in the outside, objective world, and reasons things off of observed behavior, how they actually are, as opposed to following their systems. Te types can often collect different types of “facts” or "evidence”, and then they try and weigh those side by side to make a comparison, and eventually a decision (exactly like what I’m doing now, this is Te.)
Here are both short Socionic and MBTI definitions of Te and Ti. Note that they are somewhat different.
Jung's function: Introverted Thinking
Socionics function: white logic - logic - logic of correlation
objective, outwardly measurable relationships between objects - laws, regulations, rules, categories, quantifiable properties, logic, analysis, belonging, authorship, hierarchy, subordination, objective judgments
Reality, detail, detailed study, carefulness, severity, place in hierarchies, laws, decisions, instructions, a choice of the best variant, logic of the organization,
Negative (long range):
abstraction, generality, universality, system, classification, typology, the general laws, objectivity, true, validity, the analysis, logic of a science, criteria.
Jung's function: Extraverted Thinking
Socionics function: black logic - profit - business logic
external activity of object - actions, events (what, how, where), facts, activity or work, algorithms, procedures, logic of objects’ measurable outward behavior
Advantage, benefit, profitability, technology, the facts, purchases, accumulation, the purchase, savings, putting in order, a practicality;
Negative (long range):
Uselessness, unprofitableness, use, application, deterioration, charges, expenditure, risk, experiment, sale, trade, actions in conditions of chaos, an ingenuity.
Introverted Thinking - Analyzing, categorizing, and figuring out how something works. Introverted Thinking often involves finding just the right word to clearly express an idea concisely, crisply, and to the point. Using introverted Thinking is like having an internal sense of the essential qualities of something, noticing the fine distinctions that make it what it is and then naming it. It also involves an internal reasoning process of deriving subcategories of classes and sub-principles of general principles. These can then be used in problem solving, analysis, and refining of a product or an idea. This process is evidenced in behaviors like taking things or ideas apart to figure out how they work. The analysis involves looking at different sides of an issue and seeing where there is inconsistency. In so doing, there is a search for a "leverage point" that will fix problems with the least amount of effort or damage to the system.
Extraverted Thinking - Organizing, segmenting, sorting, and applying logic and criteria. Contingency plaiming, scheduling, and quantifying utilize the process of extraverted Thinking. Extraverted Thinking helps us organize our environment and ideas through charts, tables, graphs, flow charts, outlines, and so on. One woman labeled the shoeboxes for her 100 pairs of shoes for color, height, style, and comfort. Sometimes the organizing of extraverted Thinking is more abstract, like a logical argument that is made to "rearrange" someone else's thinking process! An example is when we point out logical consequences and say, "If your do this, then that will happen." In written or verbal communication, extraverted Thinking helps us easily follow someone else's logic, sequence, or organization. It also helps us notice when something is missing, like when someone says he or she is going to talk about four topics and talks about only three. In general, it allows us to compartmentalize many aspects of our lives so we can do what is necessary to accomplish our objectives.
4. MBTI people don’t admit that their functional ordering is wrong.
People have been using Meyes’ functional model for so long that they don’t even see where they contradict themselves anymore, yet it’s there in plain sight. This is one example of Introverted Sensing (in MBTI terms), written by Lenore Thompsen (I’ll just post a segment here.)
EDIT/// I had to remove the segment here upon request... if anyone wants the link, I could still pm it to you. I'll still leave my interpretation of it here, though:
She is contrasting the ESxJs and the ISxJs. You can go through and look at how she compares them, and notice there is actually differences between Si and Se in these descriptions (at least in the way that Socionics defines it). One example she gives is how the two types are different in maintaining the “status quo”. She claims that the ISxJs are more stable with it, while the ESxJs actually change as it fits. This can easily be explained by the differences between Se and Si. We know that the Se function respects the status quo, because you can see it as it compares in the ESxP types and the ISxP types. It’s not uncommon to see ESxPs appeal to authority, or suck up to their superiors, and at least play the role of the good guy to keep things in order. ISxPs are the opposite (even MBTI descriptions will tell you that!). In a weird way, the ISxPs are actually more similar in regard to their sensing function with the ESxJs then the are with the ESxPs, although MBTI typology models ignore this. What was described here is the difference between the Si-Ne and the Se-Ni axis. They also mentioned how ISxJs often feel like they weren’t “different” in anyway, whereas the ESxJs felt more “odd” in the way that they do things. Again, Ne-Si axis as compared to the Se-Ni axis. You can check this one, too, by comparing them to their perceptive cousins.
5. No matter how you try, the models never equate, ever.
People talk about the dominant functions all the time, but they often forget about the third and fourth functions in the models. For example, an ENTP in MBTI has the order of Ne-Ti-Fe-Si. In Socionics, it is, Ne-Ti-Se-Fi. The ENTJ in MBTI is Te-Ni-Se-Fi. In Socionics, it is, Te-Ni-Fe-Si. You can see, there is somewhat of a split between the models. An example of an Introvert would be ISFP (MBTI), Fi-Se-Ni-Te, whereas in Socionics it is, Si-Fe-Ni-Te. The ISFJ (MBTI) is, Si-Fe-Ti-Ne, and in Socionics, it is Fi-Se-Ti-Ne. Again, you can see that none of the functional model translate 100%. There are a ton of little nuisances to consider, as it is not black and white.
6. Models can’t explain everything!
Most people have a hard time determining their type in the first place, let alone try and pinpoint every function they are conscious of using. Remember, models themselves are limited. They are an attempt to describe the microscopic world, on the macroscopic level. They are generalizations, simplifications, and often times wrong. It’s a fact of life, so we can't sit back and let the models describe everything, as they are merely a guide.