The typology of Myers, Briggs, and Jung is best known via the MBTI, the Myers-Briggs Type Indicator. This test can be considered separately from the Jung-Myers-Briggs (JMB) typology that it’s based on. First let’s consider the JMB typology, and then the MBTI.
The JMB typology developed from Carl Jung’s 1921 monograph Psychological Types (The Collected Works of C. G. Jung, Vol. 6), which he developed for use with depth psychology. Isabel Briggs Myers and her mother, Katharine Briggs, expanded Jung’s typology and adapted it for their test, the MBTI, in 1942.
Jung distinguished two general attitude types, extroversion and introversion, and four function types: thinking, feeling, sensation, and intuition. This resulted in eight psychological types, which Jung described mainly from literary examples.
Myers and Briggs modified Jung’s concept of intuition somewhat, which Jung had described as the “function that allows us to see around the corner of the future,” like hunches. Myers and Briggs emphasized that intuition involves the ability to recognize patterns and possibilities.
Jung’s eight psychological types focused on the dominant function but he also wrote about the auxiliary function, which Myers and Briggs included in their typology. They made explicit a distinction between perceiving and judging functions, too. The result is four binary distinctions within their typology: extroversion or introversion (E/I), sensing or intuiting (S/N), thinking or feeling (T/F), and perceiving or judging (P/J). This is the JMB typology.
The MBTI is a test instrument to determine one’s JMB type that was developed by Myers and Briggs in the 1940s. It is popular with consultants and the public but panned by academically-oriented psychologists. The main problem with the MBTI distinctions (except extroversion/introversion) is that most people are in-between, so it is difficult to tell which side of a distinction people are on. This makes it difficult for some people to fill out the test and retesting can result in a different classification.
However, this is only a problem when something else is expected, such as a bimodal distribution with two very different groups of people and few in-between. The MBTI is designed for the JMB typology which does not promote a bimodal view of psychology even though it uses binary distinctions. Healthy people can and should have the ability to use all four functions in either dominant or auxiliary mode. What the MBTI does is help people to discover which way they prefer to be, which requires a fair amount of self-awareness.
In the end the MBTI isn’t sufficiently sensing-thinking for people who prefer those functions. It tends to attract intuitive and feeling types of people. That is rather consistent with the MBTI though, which shows how it is more useful than experimental data might allow. The MBTI promotes greater awareness of oneself and others, for which people are right to consider it a handy instrument.