Hypocrates, the Greek "Father of Medicine" and first recorded Western thinker on personality, stays with us through the Hippocratic Oath: to strive to help people, or at least "do no harm."

Why do we use certain personality models and not others? Hypocrates' oath suggests that a model should not only be accurate and useful, but also healthy, promoting well-being for all individuals and not marginalizing. It reminds us to attend to the effects of our models on clients, and thus helps us decide which models to use.

For some people, "type" refers to Jung's original notion of "functions in their attitudes." For others, type means the measuring instrument that goes with type theory, the MBTI, which has extensive history and hard work behind it. Some also use temperament. And interaction or "social" styles are also fitting for people. But why don't we use the academically-blessed 5-Factor model? Or the Enneagram? Or Freud? In fact, why not have ISXX types, FTJ's or ENFQ's? One answer is that our personal experiences (a.k.a. empirical observations) suggest our models are good. The history of model-building in science also tells an important story.

In antiquity, mythic stories of gods and evil spirits explained behavior. Out of this emerged Greek philosophy. The Greeks had reason, limited world knowledge, and simple physical measuring devices. But important ideas took root. Are there categories of people? Is surface behavior (extroverted, neurotic, tidy, absent-minded) caused by underlying hidden mechanisms? How do body, mind and social interaction inter-relate? By the 1600s, many philosophical ideas gave way to "laws" described by mathematical equations. Most equations were simple and linear, such as describing what happens when one ball hits another. Eventually, psychological theories around 1900, like Freud's, caught up with and borrowed this mechanical understanding of nature. By then, however, hard science was moving on to statistical tools. Statistics allows us to consider large numbers of people or objects at once, and suggests likely patterns from data. Unfortunately, statistics suffers limitations:

• Statistical patterns necessarily only apply to groups, not individuals.
• Indirect or "non-linear" interactions are hard to get at (a.k.a. 2nd, 3rd and 4th order interactions between variables.)
• Statistical methods do not fit with how people really make predictions or decisions in psychological tests.
• Failure to explain underlying causes of surface behavior.

Today - The social sciences use statistics, whereas the physical sciences and engineering have almost completely moved on from statistics except in special areas. Instead, the mathematics of "dynamical systems" is used to construct, test, apply, and assess models. Dynamical-systems is the math-side of what is often called systems thinking.

Today, there is a wide range of specific mathematical tools to explain phenomena that are too hard for statistics, and systems addresses at least four important phenomena:

Attention to process - How things happen over time and space. Animal populations shift, global climate moves in patterns, people interact with flexibility. For example, yesterday I was quiet, tonight I am talkative - are these different behaviors? Or is there an underlying mechanism (need, value) that drives me toward both? There are computer programs that simulate human interactions based on type models. Using systems approaches, we know we have a working model when we set our computer model in motion and human behaviors happen in a recognizable big-picture way. Or, temperament theory predicts how behavior happens in a pattern, such as certain stressors for each temperament leading to survival games. Anyone can experience constraint, lack of belonging, insincerity, or incompetence, but for Rationals, only incompetence leads to mindlessness or obsessiveness.

Attention to pattern - Evaluating pieces in terms of other pieces. For example, Guardian needs and values include tradition, responsibility, group membership, safety and security, and structure. Seeing patterns means paying less attention to individual words and more attention to the overall theme that the words imply, taken together with how they inter-relate. So "responsibility" has many meanings, but when read with words like tradition, safety and structure, a "managerial" or "protective" responsibility is implied. The same with seeing whole-type patterns. INTJ doesn't mean 4 letters "interacting" with each other. Building upon experiences and others' empirical observations, I can see each type as a unique set of "themes." Numerous studies on "expertise" strongly suggest that multiple theories and numerous real-life examples are more important to understanding than philosophical answers, linear rules, single models, or statistical results.

Systems also includes structure - the brain's biological mechanisms - and purpose - including morals and ethics. Structure explains why some models are focal and others less so. Purpose links back to Hypocrates' Oath. Type is more than academic inquiry. It has a human role.

The 16 types are different but equal in quality with unique potential. People who find their true Self get energized and start growing again. Knowing that I have TJ or IT in my 4-letter code has been useful for a few specific job and relationship behaviors, but most meaningful is the whole-type "INTJ" theme. Similarly, I like temperament because it presents 4 equally healthy and very rich patterns. Rational doesn't mean NT. There is a systemic picture about learning, working, stress, relationships, play, communication style, survival games, and so on. Similarly, Jung's functions in their attitudes account for mental processes and facilitate growth. Interaction/social styles also captures my interest - ISTP, INTJ, INFJ and ISTJ are all "Chart the Course" folk. And the MBTI is really amazing considering everything it tries to get at and honor, and that it can relate to all these models!

Systems is also why I don't use other models. Either they try to compress all of human nature into a single model. Or they do not illuminate patterns or processes. Or the categories lack richness or are biased (and thus cause harm.)

To me, psychology's purpose is not to classify people or cluster surface traits, it is to treat each other better because we understand them and have a working knowledge to improve interactions. And systems thinking provides legitimacy and tools for these broad concerns.