The intellectual level of the profile is read through two independent properties: intuition, the imagination, and logic, the reasoning. Each can run from almost nothing to almost everything, and they do not depend on each other. Two things follow from the pair. How much you have of both, added together, is your level of mental energy. Which of the two leads is your type.
Three levels of mental energy
Practical types think in the present and reason by analogy: this is like that, so I will do what worked last time. Their natural horizon is a week to two months. They work well when there is a clear interest, a visible result and a benefit they can hold in their hand; they say less and do more; they are the people with golden hands, the masters and craftsmen who can turn a plan into something that exists.
Harmonious types think in the past as well as the present and reason by analysis. Their horizon is two months to a year: long enough to run a team, a department or a company of their own. They understand the worker's logic and the leader's intentions at the same time, negotiate the compromise that suits both, and are at their best where mutual benefit has to be found and a tactical plan has to be carried through.
Productive types think in the far past and the far future and reason by synthesis. Their horizon is years, decades, sometimes longer. They are drawn to the whole truth of a thing rather than its use; they can set a strategy for a large organisation or an entire field; and they are frequently ahead of their time, which is why they can seem odd to the people around them and why working purely for money leaves them unhappy. They earn their bread with their head, and often only see the effect of their work late, or not at all.
The method has an image for the three: the practical type is strong in the feet, standing on the ground; the harmonious type is strong in the hands, holding projects, contracts and plans; the productive type is strong in the head, seeing far and seeing the essence.
Times three ways of thinking
At each level, a person is an artistic type (the right hemisphere leads: images, intuition, the whole at once), a thinker (the left leads: words, logic, the parts in sequence), or mixed (the two hemispheres work in balance). That gives the eight: practical artistic, practical mixed, practical thinker; harmonious mixed and the thinker; productive artistic, productive mixed, productive thinker.
The team of eight
Here is the part I find most useful for anyone who leads people. Every intellectual type has one job that it does better than any other, and a new idea travels through all eight of them on its way to becoming real. The productive artistic type has the idea. The productive mixed type tests whether it can live, and builds the strategy. The productive thinker calculates whether it works and what it will yield. The harmonious mixed type, the great communicator, gathers the people who can make it happen. The thinker writes the tactical plan and checks it is followed. The practical artistic type builds the first working model. The practical mixed type directs the execution. The practical thinker carries it out and finishes it.
Each of them is irreplaceable, and each is at their most effective, and least tired, doing their own part. When one is missing, the idea stalls somewhere on the way, and everyone wonders why. When a person is asked to work permanently in another type's mode, they feel a tension they cannot name. Most of the friction in teams, and a good deal of the exhaustion, comes from exactly this. Knowing your own type, and the types around you, is the fastest way I know to fix it.