What's the difference?
Compared to the difference between astrology, or even other non-Jungian based theories or methods of classifying personality, there isn't much difference at a superficial level. However, there are some major practical differences and a large theoretical difference between the two bodies of work. The first essential difference is that Keirsey describes observed long term behaviorial patterns, Myers often describes what people have in mind. The second essential difference is Myers used a linear four factor model to characterize "invariant" patterns of behavior of the individual throughout their lifetime, whereas Keirsey uses a systems field theory model to characterize these patterns. Lastly, the problems of intelligence and madness, that is, what are they are and how they relate to temperament, was not effectively addressed by Jung or Myers.
To illustrate graphically, the difference between the two bodies of work, one can look at the following simplifications of how the each theory represents the "temperament" and "character" of an individual, although Myers did not explicitly address the notions of temperament and character.
One of practical problems with the defining the difference of the models is a great deal of printed or web material and books have mixed the two models together: for they are similar. Keirsey gave Isabel Myers, a layman, a great deal of credit for rescuing Jung's work and having done a great job at observing people. He related her work to other work done at the early part of the 20th century in personality not related to Jung and illustrated that these ideas about personality are quite old.
But many others have blurred the difference between "Myers-Briggs" and "MBTI" versus the published material and work of Keirsey. Please Understand Me (published in 1978), which had a significant impact in promoting "Myers-Briggs" (MBTI published in 1962, Gifts Differing by Isabel Myers, published in 1982). In fact, most descriptions found in "Myers-Briggs" books or web material are significantly based on Keirsey's Please Understand Me or his sixteen portraits that were circulated in the early 70's. Many people give a xeroxed Myers-Briggs "test", which is in fact most likely the Keirsey Temperament Sorter. There have been numerous articles on "Myers-Briggs", which actually used Keirsey's work and instruments, and attributed it to Myers-Briggs. Hence, there is a general mixing of the bodies of work.
The bottom line of the difference between the theories comes in describing the "aspects" of personality. Keirsey has done an in-depth, systematic analysis and synthesis of aspects of personality for temperament: that included the temperament's unique interests, orientation, values, self-image, and social roles. Whereas, Myers' brilliant simplifications of Jung's work facilitates the talking about four scales. For example, "Introverts" in general as a useful concept of group behavior (such as INTJ, ISFJ, INTP, ISTP), whereas Keirsey says, sorry, its more complicated than that, and if one tries to push the concept of "Introverts" too far, you will make assertions that aren't true for all temperaments.
First, let's see where Isabel Myers got her "scales" (E/I, N/S, T/F, P/J); she essentially got them by her and her mother Katherine Briggs boiling down Carl Jung's writings on personality types. Where did Carl Jung get his ideas about personality? Well, he had picked a few notions from other people and some common knowledge in Germany at the time. He picked up "Extrovert" and "Introvert" from what had been around for years, a folk psychology notion that is was latinized by some German in around 1850. Most people easily recognize that there some people much more sociable than others, the parallel of "gregarious" and "shy" are related concepts in English. Second, Jung probably borrowed the notion of tough-minded and tender-minded for William James when James discussed the mental aspects of the objective and subjective attitudes, while Jung visited with James in America. Carl Jung also discussed all kinds aspects of "the mind", and noticed that it appeared some people were better and felt more comfortable talking about abstract concepts and others seem to be better at talking about and felt more comfortable with the concrete: having to do with real objects and real people. Lastly, Jung also talked about how "the mind" appears to make decisions, some people tending toward being judgmental and decisive and others being less judgmental and flexible, but that discussion is not very visible in his book Psychological Types, published in 1923.
So, the first of major contributions of Jung was to contradict Freud and others, and say that no, *not* all people are governed by the same drives and that we are*not* all the same. Jung's second contribution was to pursue Kant's notion of "intuition" and discuss several aspects of "the mind" that involved what the mind does: perceive and abstract from world and note that each person can vary inherently in their interest in doing those two acts. Jung's third contribution was to collect a set of aspects of personality known previously and his own observations, in polar forms that seem to "cover" the space of possible "types" of people. The major contribution of Isabel Myers and Katherine Briggs was to take these contributions of Jung and made a simple linear assessment of three main aspects he talked about, then included their own scale of "J/P", and associated simple descriptions of those aspects so people could get a sense of what preferences they have as an individual.
The Myers-Briggs Type Indicator and Myers descriptions of personality did what no other personality instrument had done before, be able to give most people some insight into themselves and others. In fact, many people are amazed that by asking a few questions, the MBTI can "capture" the essence of a person's view of the world. People are surprised how accurate the MBTI can be.
However, when using this simple tool of assessment and a way of viewing one's personality, if one looks closely, there several problems that crop up.
First, people are more complex than just four numbers on four aspects of personality. But this is not the primarily problem with MBTI and Myers descriptions, this is true of all assessments, abstractions, or "theories." A model of personality is not a personality. No matter what the descriptions of personality are, they pale in comparison to the complexity of the individual. Also, the problem is not that "type" or "temperament" does not change, for the person is "changing" all the time. The difference between character and temperament (or type) of the personality help distinguish between what 'changes' and what stays the same, this is true whether one uses the Jung-Myers notion of archtypes or function types or Keirsey's notions of character and temperament.
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. For example, some talk in terms that '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 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 took her "I", "N", "T", and "P" descriptive paragraphs stuck 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 it's 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-- and other complications to the theory. However, this kind of 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. He is interested in what are the long-term behavior patterns: temperament. Moreover, Keirsey's descriptions are more integrated. He looks at the notion of personality as whole.
Next, Keirsey has a different view of the "aspects" of personality. He views them as integrated configurational form that emerges. 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* at 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".
If one is primarily viewing the world in terms of "concepts" of your own making, then clearly its important what kind of concepts are important to you. The Rationals value concepts born of their own objective (not emotional) reasoning, and the Idealists value concepts born of their own guts (emotion associated). The Rationals are pragmatic and the Idealists are credulous.
The more refined versions of Rationals include Fieldmarshals and Inventors. Both correlate to the Myers "Extrovert" letter in that they have something in common regarding their expressiveness towards the outside world. The problem is the E of ENTJ or an ENTP is quite different conceptually from the E as in ESFJ (Provider Guardian) even though some of the outside behavior aspects can be close.
The Fieldmarshall is not "extroverted" very much, and the Inventor is even less. Sure, both the Fieldmarshal and the Inventor can be "gregarious" or "not shy", in fact they can be sometimes overbearing. They are usually pretty friendly at parties and open to people to some extent. Although they don't have to be. Moreover, if Fieldmarshal is finding a particular person "boring" (and that can be in a few seconds) he quickly will find any excuse to exit the scene very quickly or rake the person over the coals, so to make sure that person realizes he is not considered worthy. So the Fieldmarshal is an "extrovert" with a purpose (they are pragmatic -- their sociability is often contingent). Sometimes that purpose can be very narrow, such that the common notion of "extrovert" is not well suited for the Fieldmarshal. Same is true with the Inventor. The Inventor often appears like an Artisan Promoter, always interested in having an "interesting" time. Only the difference is the Inventor is "looking" for new experiences, new ideas, or some way to promote his ideas, so those who don't help in this endeavor are quickly cast off. That is, the Inventor is an "extrovert" with an interest (outer-directed might be a better term), and that specific interest often being so narrow that the term "extrovert" is misleading. Although in casual acquaintance they appear to be "extroverted."
The other obvious difference between Myers and Keirsey is the classification and characterization of the concrete types. Isabel concentrated on the sixteen types, not making a major distinction between Ns and Ss in certain type groupings (such as the Thinking Types and Feeling Types). On the other hand, Keirsey finds the distinction as being major.
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"
If one is primarily viewing the world in terms of "percepts" (nature supplied or environment supplied) then the issue of what to do with those percepts based on experience is crucial. Hence you can either take it in based on experience and experienced judgment or just take it in with no judgment and just react to it based on experience or what looks good at the time.
The problem with both Keirsey and Myers characterizing of personality for a particular individual is both the complexity of the individual and the myriad of circumstances that effects the individual: its hard to apply general descriptions to some specific examples. General descriptions, are just that, and other important aspects that can confuse the issue of "temperament" is the areas of intelligence (smartness and goodness) and madness (badness and stupidity), which are two subjects that will be addressed in Keirsey's forthcoming books: Temperament and Talent, and Dark Escape.