Prescience

"Muad'Dib gave us a particular kind of knowledge about prophetic insight, about the behaviour which surrounds such insight and its influence upon eveents which are seen to be on line.' (That is, events which are set to occur in a related system which the prophet reveals and interprets.) As has been noted elsewhere, such insight operates as a peculiar trap for the prophet miself. He can become the victim of what he knows - which is a relatively common human failing. The danger is that those who predict real events may overlook the polarizing effect brought about by overindulgence in their own truth. They tend to forget that nothing in a polarized universe can exist without its opposite being present."

- The Prescient Vision by Harq al-Ada

Prescience was the term commonly used to describe the ability to see into both the past, present and future. Some awareness spectrum narcotics allowed their users to become prescient. The spice melange was one example among many in the Imperium.

Concept of Prescience
In the Dune books there are a number of individuals that are capable of various levels of prescience. These include Guild Navigators, who used such abilities to plot a safe path for Heighliners when traveling through space. The Reverend Mother Gaius Helen Mohiam was regarded as having some degree of prescience and used the Dune Tarot to enhance it. Alia Atreides, the sister of Muad'Dib, also had limited prescience.

The Atreides
Paul Atreides started having prescient dreams in his youth on Caladan. When he was exposed to Melange on Arrakis in 10,191 A.G. his abilities were enhanced. This became even more pronounced after changing the Water of Life. As a result, Paul could see events transpiring in the distant future. Paul's prescience was so powerful that when he lost his eyesight due to a Tleilaxu stone burner, he could interact with the world around him without aid. This was because he was able to remember all the details of his vision of the future. Essentially, Paul knew where everyone would be and what they would say and do.

However, it was not until his son, Leto II came to adulthood that the full power of Atreides prescience came to fruition. Leto's Golden Path was a way in which he saw mankind surviving through the eons. He could predict the demise of the human race, so he put himself in a position where he could change its evolution. Leto knew that humanity would go down the path of The Scattering as a reaction to his enforced peace.

Some 1500 years after his death, Leto's words were found in Sietch Tabr by a Bene Gesserit Reverend Mother. Leto had predicted that the Bene Gesserit would ally themselves with the Bene Tleilax.

Ability to See One's Own Death
Despite those with prescient abilities possessing the power to see into the future, it had its limitations. Primarily, those who possessed true prescience could see their own death long before it happened. As a result, prescient individuals were prone to despair, and usually felt a sense of loss for their humanity.

Inability to See Other Prescient Individuals
Paul Atreides discussed his inability of prescient individuals from "seeing" each other. Essentially, oracles were "mutually blind." This is why the plot between the Bene Gesserit and the Spacing Guild took place with Edric, a prescient Guild Navigator, present. Additionally, people who shared the aims of other prescient people were hidden from view. The one exception to this was the God-Emperor: he was capable of not only seeing the future, but seeing other prescient individuals.

Siona and Her Descendants
Leto II specifically bred generations of people to create an individual who was invisible to prescient viewers. Siona Atreides was this individual. Although not prescient she was invisible to prescient sight. This was also true of those descendants that carried her genotypes.