“Fair Witness” is a fictional profession invented for the novel, Stranger in a Strange Land, by Robert A. Heinlein. In the novel, a “Fair Witness” is an individual trained to observe events and report exactly what he or she sees and hears, making no extrapolations or assumptions. An eidetic memory (the ability to vividly recall images from memory after only a few instances of exposure, with high precision for a brief time after exposure) is a prerequisite for the job, although this may be attainable with suitable training.
In Heinlein’s society, a “Fair Witness” is a highly reputable source of information. The character Jubal Harshaw employs a Fair Witness, Anne, as one of his secretaries. Unlike the other secretaries, she does not use dictation equipment when Jubal speaks, and can keep track of several works at once, despite Harshaw’s frequent switching among them. Fair Witnesses are prohibited from drawing conclusions about what they observe. As a demonstration, Harshaw asks Anne to describe the color of a house in the distance. She responds, “It’s white on this side”; whereupon Harshaw explains that she would not assume knowledge of the color of the other sides of the house without being able to see them. Furthermore, after observing another side of the house she would not then assume that any previously seen side was still the same color as last reported, even if only minutes before.