Anteperciperation was a specific type of magic used to aid in observation and collecting of obscure knowledge, specifically events that have not happened yet, as opposed to perciperation which covers past events. It mostly utilized a specific method of scrying that enabled practitioners to witness visions and events of the future. Using this technique, a magic user skilled in perciperation could access the Ethereal Plane and glean information that was out of reach to all others. The ancient school of the I'dunal were masters at this, though viewing future events was considered notably more difficult than past events.
Utilization
Perciperation was achieved by first accessing the Dream Lay, whereby the scrying individual could transport themselves through time and space inside the lay. They did this by focusing intently on the target and honing in on it. Students were taught to first practice perciperation on "nearby" memories, meaning very recent and very close in spacial proximity. After much practice, they could learn to travel farther, both in time and distance. Once a student was able to achieve this, they could theoretically use the same techniques to access "future memories." The problem with this, however, was that these visions were notoriously unreliable, as there was always the possibility that they could change (as opposed to past memories that existed in the Ethereal Lay, which only changed depending on who you viewed them with).
Modern Usage
The hermit Master Ald uses perciperation from the safety of his cavern hovel to create his historical archive, which he then teaches to his apprentice, Gerrodine Marswan. At one point, Gerrodine gets the idea to try accessing memories that have not yet happened, where she discovers she is capable of anteperciperation.