Any time you talk about psychology or psychiatry, you don't have to get very far before you start facing deep definitional issues. While these professionals may have a few words to describe way that a person is mentally distinctive that are more unambiguously defined than common place descriptions, these are anything but exact sciences.
One important cause of this problem is that the professional researchers in psychology, usually with PhDs or M.D.s, usually in a university or privileges at a teaching hospital or mental institution, are not the people in our society who are experts at understanding other people.
Their methodologies reflect these predispositions. Subjective, adjective filled questionaires, filled out by individuals isolated from others at the time it is being completed, are their tool of inquiry of choice. The professors rarely have sustained and rich relationships with individual students. The clinicians rarely see their patients outside their offices. Psychologists also tend to be fans of sometimes dubious laboratory experiments.
Their deficits of experience may be tolerable in the area of abnormal psychology, where people exhibit symptoms that are so unusual that very few individuals have the depth of personal experience to have repeatedly encounted the symptoms in daily life. And, even when you do encounter someone with an abnormal psychological condition in your daily life, you can't only catch it with an attention to detail every bit as honed as that of a zoologist looking for chameleons. People often make every effort to be undetectable if they can help it.
But, there are other people who are much better suited to understanding normal psychology. When the "Big Five" personality traits, referred to in another blog today were formulated, the psychologists went not to people who knew a lot about people, but to dictionaries. Then they tried out the dictionary words on lots and lots of people in paper and pencil tests to "empirically" study the patterns that emerged.
What you really want to understand normal psychology is people who have particular insights into who large numbers of people are that is developed in rich, multifaceted and sustained inteactions. You want sports coaches and art teachers and music teachers and gym teachers and scout masters (and even elementary school principals (middle schools and high schools are too large to develop the right kinds of inteactions) who have interact with scores or hundreds of students at any given time and interact with the same kids multiple times a week, for many years on end, in something approaching a natural environment. You want members of the clergy who serve reasonable small, reasonable stable groups of worshippers for decades on end and see children with parents, children with friend, and so on. You want extraverted neighborhood gossips, military senior sergeants, county level political party officials, and hair stylists. You want long time members of social clubs and PTA parents. You want theatrical directors. You want general contractors and realtors. Ideally, you would prefer that they not be unduly contaminated by the formal study of the behavioral sciences.
Rather than going to a dictionary and trying to fit fuzzy concepts like personality into a pre-conceived multi-dimensional construct, you would like people like this, who have rich personal knowledge drawn from experience about the behavior of the hundreds of people that they know and you would like to ask them: "Group these people into three to sixteen clusters of people with similar personalties, however many you think you need to adequately categorize them." Ideally, you have multiple people who all know the same people classify the same group of people. This should be your starting people for fleshing out the boundaries of "personality space." Some clusters are going to be larger, and some are going to be smaller. You can ask the people who made the classifications what it is that these people have in common, how different groups differ from each other, and what observable are most valuable in making the classification. You can see if these "experts" tend to make a similar number of groups from the same group of people, and if not, if certain groups in one classification overlap with certain groups in another.
Start with people who actually know people, even if they have trouble articulating what it is that they know, and you are much further on your way that the methodologies so common in the field today.