The primarily problem with Myer's method of description is the problem of trying to take the "personality" or more specifically what Keirsey calls "temperament" (as opposed to Myers "type") and break it into four "independent" aspects. There is great utility in thinking about them as "independent" aspects, as people who follow the line of Myers are wont to do. The "Ts" tend to be like this, the "Fs" tend to be like that. The "Es" tend to be like this, the "Is" tend to be like that. This kind of talk is fine up to a point. This is where Keirsey and Myers-Jung followers part company. The problem comes in when some "Es" are different (such as the Provider Guardian "ESFJ") from other "Es" (such as Fieldmarshal Rational "ENTJ") because of temperament. The scales are not independent of each other. Of course, we are *not* talking about the myriad of other factors that complicate the analysis of personality, which includes gender, culture, etc. Those complications are another matter, irrespective of how to characterize "temperament".
Jung (hence Myers) viewed Introvert/Extrovert scale as a strong aspect, so much so that they talked about Introverted Thinkers and Extroverted Thinkers (we will let the reader speculate out what they meant by these phrases). Keirsey, on the other hand, regards Jung's N/S "scale" as the first "cut" (which of course in reality we "can't" cut the temperament into pieces). In other words, "how" one's mind primarily processes the world (through concepts or percepts) is the major determinant on how one evolves and reacts in life; not, whether one is more or less comfortable with people. As an example, Albert Einstein (INTP) is quite different from Clint Eastwood (ISTP). On the other hand, if one tries to "talk about" what is "in the mind," one can start talking nonsense because we can't observe "mind".
Moreover, Myers in her descriptions mostly treat the personality aspects as independent scales. Her descriptions of the sixteen types, essentially is a concatenation of the aspects. She has a descriptive paragraph for "I," and a paragraph for "E,", a paragraph for "N," and so on. To get her descriptions, for example, an INTP, she takes her "I", "N", "T", and "P" descriptive paragraphs sticks them together and "viola" you have a full description of a person (an INTP). The problem with this Chinese menu method of personality, is that its too simplistic. Partly to fix the problem of it being too simplistic, Myers and her followers tried to work in the notion of shadow or dominant functions, however, the speculation of "what's in mind", becomes complex and confusing, and worse of all, hard to remember.
Keirsey is not concerned with "what's in mind", but what people do. What are the long-term behavior patterns: temperament. Keirsey's descriptions are not as much of a cookie cutter form as Myers-Briggs. His descriptions are more integrated. He looks at the notion of personality as whole. Thus, given that N/S is the "first" cut, the descriptions might be viewed as in a tree (or as an unfolding (emergence) of individual's temperament). As in the following. The lower level is constrained by the configuration above it.
"Ns" What Jung called "iNtuitives". Keirsey liken them to "Martians." Abstract. Introspective. Those who look *primarily* through their *own* "minds eye."
"Ss" What Jung calling the aspect "Sensing" Keirsey liken them to "Earthlings" Concrete. Observant. Those who look *primarily* to the world by their "percepts", using what's out there.
Second cut of the Ns
"NTs" Myers called them "iNtuitive Thinkers" Keirsey calls them "Rationals".
"NFs" Myers called them "iNtuitive Feeler" Keirsey calls them "Idealists".
Second cut of the Ss
(Myers or Jung never thought of using different criteria for different parts of the tree, because they didn't view it as a tree)
"SPs" Keirsey calls them "Artisans"
"SJs" Keirsey calls them "Guardians"