In Herbert's fiction, following the defeat of the thinking machines by humanity in the Butlerian Jihad, it is forbidden to create sentient machines. The Mentat discipline is developed as a replacement for computerized calculation, just as the Bene Gesserit and the Spacing Guild take on functions previously performed by thinking machines. For thousands of years, society considers Mentats the embodiment of logic and reason.
Unlike computers, however, Mentats are not simply calculators. Instead, the exceptional cognitive abilities of memory and perception are the foundations for supra-logical hypothesizing. Mentats are able to sift large volumes of data and devise concise analyses in a process that goes far beyond logical deduction: Mentats cultivate "the naïve mind", the mind without preconception or prejudice, so as to extract essential patterns or logic from data and deliver useful conclusions with varying degrees of certainty. They are not limited to formulating syllogisms; they are the supreme counselors of the Dune universe, as menial as an economist or a historian who might advise leadership, or as grand as advisor to the Emperor. So the Mentat is not a purely "left brain" type of intelligence with only a simplistic-autistic cognition, they are profoundly aware of nuance, subtlety and the kind of "sensitivity to initial conditions" which is studied in Chaos theory. Additionally, they take in information through visual as well as other media and their calculations are delivered not as numerical probabilities but as flowing paths, subject to new variations through the influence of new factors.
A Mentat's capabilities can be greatly increased by taking sapho juice, but using it leads to addiction. Sapho is extracted from roots found on Ecaz, and its use doubles or even triples the Mentat's already immense processing power. Repeated use leaves a permanent "cranberry-colored stain" on the user's lips.
Being a Mentat can be a profession in itself, or the discipline can be added to other roles. Few people have the ability to be a Mentat; thus, those with the discipline are prized in whatever role they choose. There are also varying degrees of ability. In Dune (1965), Thufir Hawat is considered to be one of the best Mentats of his time. Paul Atreides is a Mentat duke (and later emperor) in Dune, and in Heretics of Dune (1984) and Chapterhouse: Dune (1985), Miles Teg is a Mentat bashar (or general) and the most formidable military commander in the known universe. In Dune Messiah (1969), Duncan Idaho is recreated as a ghola and trained as both a Mentat and a Zensunni philosopher. In Children of Dune (1976), he marries the Regent, Paul's sister Alia, but is then instrumental in protecting the royal heirs from her, demonstrating that Mentats are rarely simply disinterested observers and counselors.
It is also possible to vary the discipline: In Dune, the Tleilaxu create "twisted Mentats" for Baron Vladimir Harkonnen (Piter De Vries being the most notable example). These are sociopathic Mentats free from the usual constraints of human morality or instinctual considerations (Piter is, among other things, a sadist, and acts as torturer for the Baron). In Heretics of Dune the Tleilaxu supply the Bene Gesserit with a Duncan ghola they have altered in many subtle and hidden ways, including the addition of submerged Mentat abilities.
In God Emperor of Dune (1981), Leto II outlaws the order and crushes any renegade training schools he finds. Unlike his execution of historians, done to control his legacy and symbolism, Leto never says why he suppresses Mentats, leaving the reader to conclude that it simply plays a role in his larger purpose of oppressing humanity in order to create his Golden Path. The art is not eliminated, however, surviving through underground schools; notably, the Bene Gesserit preserve the art, assuming that Leto knows of this (through his prescience) and approves.
I went to Wallach IX at the Tyrant's command ... My orders were to suppress the Mentat school you thought you had hidden there ... I, a Mentat, forced to suppress a school that trained people the way I was trained. I knew why he ordered it, of course, and so do you.
Bellonda retrieves the following information from Other Memory:
Order of Mentats, founded by Gilbertus Albans; temporary sanctuary with Bene Tleilax who hoped to incorporate them into Tleilaxu hegemony; spread into uncounted "seed schools"; suppressed by Leto II because they formed a nucleus of independent opposition; spread into the Scattering after the Famine.
The origin of the first Mentat is later explored in the Legends of Dune (2002–2004) prequels written by Kevin J. Anderson and Brian Herbert. During the Butlerian Jihad, thinking machine leader Omnius sees humans as animals, but the independent robot Erasmus argues that any human can become brilliant. Omnius picks a nine-year-old, blond-haired boy who appears to be the wildest and most unkempt of all, and challenges Erasmus to prove his theory. Erasmus calls the boy Gilbertus Albans, thinking that this sounds like a smart human's name. After initially failing to make progress by using a system of benevolence and rewards, he switches to a system of strict supervision and punishment, and the method works. By emulating Erasmus, whom he has come to consider his father, Albans becomes the first to display computer-like cognitive and calculation capacity on the level of thinking machines.
To his own surprise, Erasmus also develops an attachment to the boy; when Gilbertus is about 20 years old, Erasmus performs a life-extension procedure on him without permission from Omnius. Because of Gilbertus' remarkable memory-organizational ability and capacity for logical thinking, Erasmus nicknames him "Mentat," created from the words mentor, mentee and mentation. During the Battle of Corrin, Erasmus deactivates an explosive trip mechanism in the thinking machine defenses in order to save Gilbertus, thereby dooming the entire machine empire. Afterward, the robot declares:
Perhaps when all the thinking machines are gone, you can teach your fellow humans how to think efficiently. Then all my work will not have been for nothing.—Erasmus, Dune: The Battle of Corrin (2004)
In this way the thinking machines are retconned as the creators of the Mentats, who remain the machines' enduring legacy to human civilization. Amidst the fanatical anti-computer culture that took permanent root throughout all humanity, the Mentats thrive from being an accepted substitute over intelligent technology, with the Mentats' actual origins completely unknown to all humans.
It is by will alone I set my mind in motion. It is by the juice of sapho that thoughts acquire speed, the lips acquire stains, the stains become a warning. It is by will alone I set my mind in motion.
This mantra is a creation of Lynch and does not appear in the books, though in Dune there is mention that Thufir Hawat has cranberry-stained lips from sapho juice.
Other works of fiction
The Marvel Comics character Mantis has been referred to as possessing "mid-range mentat" training since reappearing in the Annihilation: Conquest storyline, and has performed heightened acts of cognition and calculation since (in addition to her telepathic, telekinetic, and precognitive powers).
In a non-canon 'help corner' of the video game BlazBlue: Continuum Shift the "Mentat plant" is a strange, black-colored spherical plant that supposedly increases intelligence.
In the video game series Fallout, "Mentats" are a health item which improve mental attributes but also present the risk of addiction with every use.
In the John Ringo Novels Sister Time and The Hero, the title of "Sohon Mentat" appears as a rank for high level masters of psychic manufacturing amongst the alien Indowy race. In Sister Time it is referenced as having been drawn directly from Dune.
- Herbert, Frank (1965). Dune.
- "Paul looked at his father, back to Hawat, suddenly conscious of the Mentat's great age, aware that the old man had served three generations of Atreides. Aged. It showed in the rheumy shine of the brown eyes, in the cheeks cracked and burned by exotic weathers, in the rounded curve of the shoulders and the thin set of his lips with the cranberry-colored stain of sapho juice." Dune
- Annihilation: Conquest: Starlord #1, Marvel Comics, 2007.