People often ask me about various other ‘temperament’ models and how they relate. Years ago (in the pre-internet mid 1980’s) when I was going to the post office frequently to mail my dissertation drafts back and forth to David Keirsey for review, the postal clerk asked me what I was mailing so often. Then he asked me what it was about. When I told him temperament, he said his wife had one of those! Over the years as I’ve researched more and more about temperament I discovered that in general the term means something different in the mainstream psychology literature than the way David Keirsey wrote about it Mainstream Definition Classic ‘temperament’ theory goes back to the belief that there were different humors in the body, blood, phlegm, yellow bile, and black bile that were at the root of differences in human behavior. There was a search for physical basis for behavior. Over the years, longitudinal studies have been done with children into adults and certain characteristics seem to have remained throughout the research subjects’ lifetimes. The most researched characteristics have been with the Eysenck definitions of introversion and extroversion, with support for there being a biological basis for these...