This is the forerunner of many contemporary works on psychological types. The mother-daughter team of Briggs & Myers devised the Myers-Briggs Type Indicator (MBTI) on it--devising the 4th (Judgmental-Perceptive) scale based on preferences (i.e. superior function vs. secondary function) between the iNtuitive-Sensate scale & the Thinker-Feeler scale. Jung does not address the J-P scale (it didn't exist yet). The book is written in Jung's usual rambling, erudite style with his usual quantity of incredible interspersed observations & conclusions. Some modern works are far easier to read, but many (e.g. Keirsey's "Please Understand Me") leave much out. Indeed, his assessment tool is quicker but less accurate IMHO (I used to score MBTI results for a professor doing research on MBTI's in other countries). I also took a couple of short courses (paid for by the U.S. Navy) related to the MBTI--& lots of management courses which referred to it or utilized it. It is extremely useful in improving interpersonal communications & understanding amongst co-workers, supervisors, etc. I used it with my own subordinates & found it quite valuable--people shared their results readily. Of course, there's a bit of confusion between Extrovert & Introvert--surface/laymen views can be misleading. The key is where one gets/loses one's psychic energy. Introverts get it from being alone & tend to lose it in groups; Extroverts, vice versa. But, this has nothing to do with whether one enjoys people, books, parties, etc. So, to understand the types, one must read the book. As Jung states, p. 526 "The psyche is the very thing we know least about, although it seems to be what we know best of all, & furthermore that everyone else probably understands it better than we do ourselves." Further, self-knowledge is a continuing challenge because p. 52: "The psyche creates reality every day." Also, psychological type relates not only to self, but also to society: p. 448: "Only a society that can preserve its internal cohesion and collective values, while at the same time granting the individual the greatest possible freedom, has any prospect of enduring vitality" & p. 449: "The more a man's life is shaped by the collective norm, the greater is his individual immorality." However, it is important to understand that Jung is NOT saying people ARE this type or that (implying the types are real) but that the types are a useful model for understanding human differences-- p. 493 "Reality neither consists of theories nor follows them." The sixteen types are a reasonable model for differences in accordance with Jung's scientific approach. As he states here & elsewhere--on p. 41 & on p. 494ff: "The scientific axiom known as Occam's Razor--`explanatory principles should not be multiplied beyond the necessary.'" Necessary & sufficient are required. This work is at least as relevant today as when it was written.