It occurred to me that here I am, spouting off my ideas about personality type without any sort of credibility, so I thought I'd provide a window into my background as an armchair personality theorist.
It all began in college when I was given a variant of the MBTI (Myers-Briggs Type Indicator). I don't think it was the real deal--nonetheless it pegged me accurately, though I was tied on I and E, and it wasn't until after graduation when my social life slowed down that I realized I was truly an introvert, though I suspected that all along. Anyway, that initial exposure to personality typing made me eager to learn more, and that's what I've been doing (on and off) for the last 15 years.
In addition to reading about personality types, doing a few seminars for church and school groups, last fall I took a workshop to become a qualified MBTI practitioner, so now I can finally administer the authentic assessment and do it correctly (one of the major reasons why people reject personality typing is because they've had an experience where essentially they had their fortune told--i.e. 'take this test, here's your four-letter type, that's what you are, end of story'). It's a much more complex process than that. It's also not one-dimensional, which means those four letters actually need to be expanded into the 8 functions they comprise. Despite all my research, I really didn't get a full grasp of the 8 functions until I took the workshop, and I'm still learning more about what each one means.
When I say 8 functions, I mean this (we all use all of them, but our four letter types determine the order in which we prefer--consciously and unconsciously--to use them):