This category deals with how we prefer to interact with the world and how we prefer to get our energy and stimulation. Extraverts are energized by other people and action. They are talkers, often thinking out loud, interrupting people at meetings, or bursting into a co-worker's office to ask an opinion, and then not really listening to it. Extraverts become drained when they have to spend too much time alone; they need other people to function. Introverts, on the other hand, get their energy from their own thoughts and ideas, rather than heated discussions. Introverts rarely speak up at large meetings, preferring listening to talking. Introverts need alone time, especially after spending a few hours with people.

Introverts are outnumbered by extraverts by about three to one in America. Extraverts are often rewarded in school, by participating in class discussions, and at work, because they are popular and outgoing. Introverts, on the other hand, are often undervalued because they keep their best to themselves.

Sensor or iNtuitive

This category deals with how we prefer to gather information about the world. As the name implies, sensors prefer to use their five senses to gather information. Sensors are quite literal, preferring facts and details to interpretations. If a hard-core sensor asks what time it is, he or she expects to hear "11:07 a.m.," and not "a little after 11" or "about 11." About 70 percent of Americans are sensors. For iNtuitives, on the other hand, everything is relative. They aren't late unless the meeting has started without them. iNtuitives look at the grand scheme of things, trying to translate bits of information, through intuition, into possibilities, meanings, and relationships. Details and specifics irritate iNtuitives.

iNtuitives see the forest; sensors see the trees. When working with sensors or iNtuitives, it is important to remember these differences. Sensors prefer to learn through sequential facts; iNtuitives through random leaps. The task- "Please sort through these surveys" - means something entirely different to sensors and iNtuitives.

Thinker or Feeler

This category deals with how we make decisions. Thinkers base their decisions on objective values, and are often described as logical, detached, or analytical. Some thinkers are thought of as cold or uncaring because they would rather do what is right than what makes people happy. In contrast, feelers tend to make decisions based on what will create harmony. Feelers avoid conflict; and will overextend themselves to accommodate the needs of others. Feelers will always "put themselves in somebody else's shoes" and ask how people will be affected before making a decision.

This is the only personality type category related to gender. About two-thirds of all males are thinkers, and the same proportion of females are feelers. There often are problems in the workplace for those who don't conform to their gender's preference. For example, a feeling man is labeled a "wimp." Much more negatively, a thinking woman is "unfeminine," she "has a chip on her shoulder" or much worse. Thankfully, nobody is 100 percent thinker or 100 percent feeler (as with the other personality types). Everyone, to some extent, cares, thinks, and feels, but final decisions are reached through very different routes, based on a person's true personality preference.

Judger or Perceiver

This category deals with how we orient our lives. Judgers are structured, ordered, scheduled, and on-time. They are the list makers. Judgers wake up every morning with a definite plan for the day, and become very upset when the plan becomes unraveled. Even free time is scheduled. Perceivers, on the other hand, rely on creativity, spontaneity, and responsiveness, rather than a plan or list, to get them through the day. They burn the midnight oil to meet deadlines, although they usually meet them. Perceivers like to turn work into play, because if a task is not fun, they reason, it is probably not worth doing.

Experts say that this personality type difference is the most significant source of tension in the workplace and in group work. Perceivers prefer to keep gathering information rather than to draw conclusions. Judgers prefer to make decisions, often ignoring new information that might change that decision. Hence, the conflict. The authors of the book contend that a good balance of judgers and perceivers are necessary for a well-functioning work group. Judgers need light-hearted perceivers to make them relax, and perceivers need structured judgers to keep things organized and reach closure on projects.