inconsistency in MBTI theory. This incompatibility sometimes (note sometimes) appears between Introvert types. As for Extrovert types - MBTI theory, Socionics and Jung seem fully compatible.

The reason for this is that when Myers was designing MBTI, she took Jungian typology as the basis for her project. According to Jung, people can be Extroverts (E) or Introverts (I), Thinking (T) or Feeling (F), Sensing (S) or Intuitive (N). So Jungian types ended up looking like this:

Extraverted Thinking type
Introverted Thinking type
Extraverted Feeling type
Introverted Feeling type
Extraverted Sensing type
Introverted Sensing type
Extraverted Intuitive type
Introverted Intuitive type

Jung also indicated that along with the main function, type could have a secondary function as well, which is different in nature to the primary function. In other words, the type with a main preference for T or F could also have a secondary preference for N or S and types with a main preference for N or S could also have a secondary preference for T or F. The two variations of the same core type would be different from each other, for instance, F type with preference for S would be different from F type with preference for N, and so on.

Myers was particularly interested in the mental processes that were dynamically opposite like E vs. I, S vs. N, T vs. F., because this would allow to formulate a bipolar question - if you prefer one thing then you do not prefer its opposite, theoretically.

Myers was faced with the challenge of how to identify which mental process would be the main and which one would be the secondary. For example if a person would show a preference for N and T, then would this be N that is the main preference and T that is the secondary, or vice versa?

If you are not familiar with Jungian work on types, there are two more definitions that Jung used to describe his types - Judgement and Perception (Some sources call it Rationality/Irrationality, perhaps due to the differences in translation). All his eight types Jung divided into two groups. Judging types became all Thinking and all Feeling types, Perceiving types became all Sensing and all Intuitive types.

Judging types according to Jung:

Extraverted Thinking type
Introverted Thinking type
Extraverted Feeling type
Introverted Feeling type

Perceiving types according to Jung:

Extraverted Sensing type
Introverted Sensing type
Extraverted Intuitive type
Introverted Intuitive type

How could this have helped Myers? Simple, if a person scores as ENT (Extravert and Intuitive and Thinking) their type could be either Extraverted Intuitive type (Perceiving group), or Extraverted Thinking type (Judging group). Which one it is, would be defined by knowing if the type was Judging or Perceiving. So everything was already concluded in Jungian research. However the preference for Judgement/Perception was not explored by Jung in his work as well as all the other preferences, so Myers decided to come up with her own Judgement/Perception scale instead. She probably figured, if people use their preferred judging process to order the external (!) world - they are Judging types, but if they use their preferred perceiving process to experience the external (!) world - they are Perceiving types.

Have a look:

Jung: Sensing and Intuition are P functions, always!
Myers: Sensing and Intuition are P functions, but only if they are extraverted!
Socionics: Sensing and Intuition are P functions, always!

Jung: Thinking and Feeling are J functions, always!
Myers: Thinking and Feeling are J functions, but only if they are extraverted!
Socionics: Thinking and Feeling are J functions, always!

Maybe Jungian definition of J and P was not clear enough to be implemented practically at once, but what was absolutely clear is that Sensing and Intuitive types he called P and Thinking and Feeling types he called J.

Now let's have a look at the official MBTI correspondence between Jungian type and MBTI type:

Jung	MBTI theory
Extraverted Thinking type Introverted Thinking type Extraverted Feeling type Introverted Feeling type Extraverted Sensing type Introverted Sensing type Extraverted Intuitive type Introverted Intuitive type	ENTJ, ESTJ INTP, ISTP ENFJ, ESFJ INFP, ISFP ESFP, ESTP ISFJ, ISTJ ENFP, ENTP INFJ, INTJ

This table clearly shows incompatibility between MBTI and the Jungian definition of J and P. According to Myers, Introverted Thinking and Introverted Feeling types appeared to be P instead of J, and Introverted Sensing and Introverted Intuitive types appeared to be J instead of P.

So, why this obvious mistake has not been rectified? First of all whether you want it or not, MBTI types obtained via MBTI test results (under ideal conditions) are actually quite compatible with Jungian type. The reason for this is that despite Myers wrongful, one-sided J/P definition, MBTI J/P questions often (not always) identify one's preference for Jungian J/P. The problem however is that there are three kinds of MBTI type profiles in existence:

1. Type descriptions empirically gathered from the observation of people who took the MBTI test. These profiles are compatible with Jungian types.

2. Type descriptions artificially manufactured based on different functions as they appear in MBTI model. These descriptions are more accurate than the previous, but they only refer to the descriptions of extravert types obtained this way. Only extravert type descriptions are Jung compatible for the reasons explained above. All introvert type descriptions are twisted around the J and P preference. So if you have MBTI description of ISFP obtained this way, for example, you should know that it is actually Jungian ISFJ description you look at.

3. Mixed type descriptions obtained via combination of 1. and 2. Extravert type descriptions are, again, compatible with Jung, but Introvert type descriptions look like a compromise between J and P types. Basically, introvert type descriptions look like one-size-fit-all descriptions.

If you are an introvert type, you are in trouble. For example, you take the test and come up J. Then you read some P type descriptions to compare and find out that your type fits P profile better then J. You look further and decide that you might be J after all. Or is it P?

The core of the problem is in Myers deciding to connect J and P with the external world, even though Jung wrote that J and P are independent of E and I. The extrovert types apparently do not suffer just as bad from this mistake.

There are two solutions to this problem:

1. A very simple solution. Let's admit that MBTI type and Jungian type are quite different, and drop all the relations between them. This will not solve the internal MBTI inconsistency problem (test results vs. modelling), though.

2. An even simpler solution. Let's finally agree that Jungian definition of J and P is the one to use. This eventually will straighten up MBTI model as for introverted types. The problem here is that so many researches and publications have been carried out using the faulty MBTI model and at the end of it all, those works will only be good for recycling purposes.

So for the time being, in order to separate the Jung compatible four-letter type acronym from the one that is not compatible with Jung, it is advisable to use a small letter "p" or "j" at the end of the four letter abbreviation. This would mean that the type is different from MBTI type and also fully compatible with Jungian theory and Socionics as well.

In conclusion, MBTI is actually one of the most popular psychometric tools of today. In fact, it is so well-known that MBTI type stands next to astrological type by its popularity. Despite this, MBTI theory has no proper method of verifying test results. The only verification tools available are the profiles of sixteen types accompanying the test. The problem with this is that the profiles are poorly written, reminding one of astrological interpretations and giving only vague answers regarding the accuracy of the test results. Sadly, MBTI is widely used to implement important decisions, including screening for employment, education, etc., which is arguably an ethical practice.

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