Jeff Orkin of Monolith gave details at GDC how the artificial intelligence in F.E.A.R. really worked. There are different styles when it comes to A.I. and it seems F.E.A.R. approaches it in a unique manner.

First of all, the AI powering F.E.A.R. was based around the idea of giving the AI a need. As illustrated by Orkin, this need could take the form of Alma (the creepy little girl in F.E.A.R.) being hungry and wanting to eat, but in terms of the game, this means something like “see player, attack player, find cover.” The actions that the AI could take to satisfy its need are strung together and happen based on the player’s actions; each action the AI can take is assigned a “cost” and the AI goes for the least expensive action.