The name "Mentat" is derived from mentis, meaning "of the mind" in Latin, an ancient Terran language. The founder of the Order of Mentats, Gilbertus Albans, a logician and philosopher of interstellar repute, coined the term to refer to those fully trained and proficient in the techniques he prescribed for the Order. For thousands of years, society thought of Mentats as the embodiment of logic and reason.

A Mentat adept could be characterized as (a) a human in the generic, Bene Gesserit sense (although the Sisterhood would deny it violently), i.e. "an animal with reason and logic;" (b) an expert in all methods of logic and inference; (c) a conceptual generalist, in contrast to specialists in narrow areas; and (d) one possessing a quasi-truth-sense based not on prescience but on inference.

The Mentat adept is of achieving remarkable inferential linkages and gestalten spasms of pure insight, but unusually only when deep in a Mentat-trance. Some allege that the so-called Mentat-trance is merely a dramatic device used to make the Mentat appear more impressive. But the subjective reports of scores of Mentats and the objective evidence of hundreds of studies all point to the authenticity of the trance. The eyes glazed, the voice-intonation flattened, and awareness appeared to be turned inward.

Perhaps because of their apparent need to rely on their isolating trance-state for higher percentages of accuracy, Mentats historically failed as leaders. A supporting argument is that leadership is a matter of temperament, not reasoning ability. The effective leader must often make intuitive decisions in the absence of complete data. A good emperor, duke, general, or director acts because a decision must be made, but a Mentat delays because a decision should not be made.

Mentat Ranks:

Minor Orders:

Memorizer: The fully prepared Memorizer is capable of retaining both related and unrelated information. The final test involved absorbing a series of 2 x 104 numbers or letters and reproducing them in correct sequence, duplicating the same timing or spacing as the original. Memorizers are able to repeat entire books from recall. They are able to replicate spatial configurations, such as the layout of a city after having seen the place (or plans of it) only once. Their chief accomplishment, however, is the ability to repeat conversations word for word from start to finish, mimicking the cadence and vocal inflection of each participant.

Processor: Processors learn to combine, divide, sort, and file pieces of discrete information with 99.99985 percent accuracy. They are capable of introducing order and regularity to seemingly unrelated sets of information. The chief danger to Processors is that the order introduced might or might not be in accord with reality. Thus, processors are trained to attempt first to use the categories and labels that others provide. This sorting, sifting, and retrieving of information, as well as the ability to connect it with specific names, places, or events, is valuable beyond estimation in the anti-computer culture of the times.

This level would be the equivalent in extensive training in Mathematics, and Research, as well as the of the Memorizer, and further study into knowledge-based skills. The Odious Personal Habit (Naive) is also appropriate to Processors.

Hypothesist: Hypothesists were trained to extrapolate from information to alternative explanations for the causes or the effects of that information. Hypothesists often prided themselves on the number of differing interpretations they could see in a set of events. The Hypothesist would naturally provide his master with at least a two-place ranking of the likelihood of the interpretations he offered. The primary hypothesis was 92 to 98 percent reliable.

Major Orders:

Generalist: If Processors seem innocent and accepting, Generalists appear haughty and pedantic. Generalists overcome the naive literalism of the junior orders by "bringing to decision making a healthy common sense," but in achieving awareness of the "broad sweep of what is happening in his universe" (and note the relativism of "his universe"), the Generalist risks believing himself supreme in his encyclopedic store of knowledge.

Generalists are expected to possess broad and accurate knowledge of at least 94.75 percent of everything occurring in "his universe;" this knowledge, joined to the confidence-building Mentat training, leads many a Generalist to annoy his comrades with an overblown sense of his own superiority. Generalists are warned that principles of expertise can change, that no one can catalogue all knowledge, and that the Generalist is himself part of the set of phenomena to be learned. But even with these caveats, Generalists are very difficult people to work with.

Simulationist: Mentats who free their reasoning from dependence on absolutes, and who can correct for assumptions hidden in another's inferences achieve the title of Simulationist. The Simulationist conceives and proposes in detail alternative futures, courses of action and explanations of events. Economic, political, and military strategy depended heavily on the unfolding of options by Simulationists: a good one can easily offer his master up to ten courses of action and what is more, infer the dozens of possible consequences of pursuing, altering, combining or disengaging any of these course. The Simulationist sees ever human being as a set of behaviour patterns ready to be orchestrated.

Advisor: Only one novice in twenty achieves the coveted sixth rank, Advisor. Skilled in wisdom and diplomacy, possessing the abilities of all the lower ranks, adding sophistication and understanding, an Advisor is the equal in price and value of a Sardaukar legion or a bloc of CHOAM shares. Advisors planned for the long run, they negotiated delicate matters, they judged matters of life and death. A Mentat-Advisor is thought to be able to transform a mediocre ruler into a respected leader, and a better-than-average ruler into a potential emperor.

Mentat Dysfunction:

Memorizer Babble, Processor naivete, and Generalist pride have been noted above. But other conditions can impair a Mentat's abilities.

Mentat Freeze: Generalists and higher-rank Mentats are vulnerable to a syndrome called "Mentat-Freeze," which springs from self-doubt. Although taught to transcend the narrrowness of specialization, no human being can be entirely free from the element of uncertainty that transcendence implies. Repeated and strenuous questioning of a Mentat's computations does not lead to new computations -- those are inferentially determined -- but to anxiety about the base of those computations. Senior-rank Mentats are repeatedly warned that wavering is the first step toward the totally disabling Mentat-Freeze. That state halts all Mentat functions permanently unless the doubt could be removed and confidence restored.

The rehabilitation of frozen Mentats consumes a long process of hypnosis, counselling, and the ultimate rebuilding of a personality strengthened to resist self-doubt. So devastating is Mentat- Freeze that the condition, even if recovery was complete, is an insuperable impediment to progress of higher rank. Recuperated fifth and sixth rank Mentats are reduced to appropriate junior levels. Mentats are often haunted by fear of freezing, particularly those who labor alone, far from the protective support of the Order House or other senior Mentats.

Sapho Addiction: Addiction to Sapho, an energizing liquid extracted from Ecaz plants, is a trap to which Simulationists both in training and in the field are most susceptible. Although Sapho amplifies speculation and extrapolation, it subjects its user to unpredictable outbursts of emotion or long periods of passivity. The Mentat-addict's lethargy leads him to neglect the constant updating of information upon which his accuracy depends.

Rhajia: For Mentats Rhajia is the song of the sirens. It is the total immersion of the Mentat in the inferential consciousness, and even the founders of the Order of Mentats disagreed on its nature. Some called it the "Movement of Infinity," and regard it as the final stage of the Order, a breaking of the chains of servitude to practicality; but others think it is a death-trap: only 30 percent of Mentats who enter rhajia "reawakened;" the other 70 percent become comatose and die. Those surviving report either no memories whatsoever or the most richly satisfying intellectual experience of their lives. Rumor has it that older Mentats near death seek rhajia as "the most pleasant passing" a human could be blessed with.

Mentat Variations:

Mentat-Assassin: The Ginaz School of Master Swordsmen provides training to Advisor rank Mentats, thus helping to create the specialization Mentat-Assassin. A valuable and necessary tool of any of the Houses Major before the reign of Leto II. Experts in the terms of kanly, and the Great conventions, a House's Master Assassin is as valuable as a legion of seasoned warriors. Besides completing all of the qualifications for Advisor rank, a Mentat-Assassin must possess a minimum DX of 14. Ginaz training would include expert level training in Beam Weapons, Disguise, Garrote, Knife, Poisons, Shortsword or Katana, Throwing, Savoir-Faire (Kanly), Staff, Stealth. The martial arts style An C'hi is appropriate for a Mentat-Assassin, as is the Weapons Master advantage.

Twisted Mentats: Tilaxu "twisted" mentats are different from normal Mentats in those characteristics nonessential to pure computational ability. These variants take the form of body structure, emotional nature, and psychological make-up, depending upon the customers orders. As a result of their genetically tailored nature Twisted Mentats can have any Advantage or Disadvantage, regardless of other character considerations. Notable twisted Mentats include: Multifest Hydros, the mentat-politician who possessed seven different personalities; Piter de Vries, House Harkonnen's effeminate psychopathic killer; Lizao Twine, the mentat- hermaphrodite whose courtesan palace disguised a notorious web of intrigue; Bliss Numera, the female mentat-monk-chemist, who for twenty-six years lived in solitary confinement, existing on vegetable broth, but failed to perfect the formulae by which to transform silverfern into melange. Some twisted mentats are more twisted than others, and a few not very twisted at all. Nevertheless, because the mentats produced by the Tilaxu are so often warped and bizarre in nature, they are increasingly regarded as objects of repugnance.