Prediction

A prediction is a statement or claim that a particular event will come to pass in the future. The etymology of this word is Latin (from prœ- "before" plus dicere "to say").

Informal prediction

Outside the rigorous context of science, prediction is often confused with informed guess or opinion. A prediction of this kind might be valid and useful if the predictor is a knowledgeable person in the field and is employing a sound reasoning and accurate data.

Supernatural

Predictions have often been made, in pre-scientific times and still today, by resorting to paranormal or supernatural means, such as prophecy, or disciplines now classed as pseudoscience, like astrology. So far none of these means of prediction have been proven under controlled conditions, though most Christians take Biblical prophecy seriously.

Scientific prediction

In a scientific context, a prediction is a rigorous (often quantitative) statement about what will happen under specific conditions, typically expressed in the form If A is true, then B will also be true. The scientific method is built on testing predictions which are logical consequences of scientific theories. A theory whose predictions are not in accordance with observations will likely be rejected. In many scientific fields, desirable theories are those which predict a large number of events from relatively few underlying principles.

Example

In the 1840s the renowned Austro-Hungarian physician Ignaz Semmelweis noticed that women giving birth in the Vienna lying-in Hospital were dying in one building, but surviving in another.

Upon considering the cause, he found that the surviving women were attended by midwives and not by student physicians. Thus he proposed the hypothesis that the physicians were a factor in the deaths.

This proposition impelled Semmelweis to refine the factor. What was the difference between the midwives and the doctors? After more thought, Semmelweis decided that the cadavers which the student doctors were touching must be part of the factor.

What could the doctors do to avoid the factor? Semmelweis predicted that, if the doctors were to wash their hands, then the cadaver factor will be avoided.

Semmelweis therefore instructed the student doctors to wash their hands, and the women who were attended by the doctors survived. Thus his prediction was successful, and his explanation was validated.

A review of the whole process:

Semmelweis, 1861. The Etiology, Understanding, and Prophylaxis of Childbed Fever.

Prediction in fiction

Fiction (especially fantasy and science fiction) often features instances of prediction achieved by unconventional means.

In fantasy literature, predictions are often obtained through magic or prophecy, sometimes referring back to old traditions. For example, in J. R. R. Tolkien's The Lord of the Rings, Elves are shown to possess an accute awareness of events, extending into the future, and sometimes appearing as more-or-less vague prophecies. The character Galadriel, in addition, employs a water "mirror" to show images, sometimes of possible future events.

In Ursula K. LeGuin's The Left Hand of Darkness, the humanoid inhabitants of planet Gethen have mastered the art of prophecy and routinely produce data on past, present or future events on request.

In some of Philip K. Dick's stories, mutant humans called precogs can foresee the future (ranging from days to years). In the story called The Golden Man, an exceptional mutant can predict the future to an indefinite range (presumably up his to death), and thus becomes completely non-human, an animal that follows the predicteds paths automatically.

In the Foundation series by Isaac Asimov's, a mathematician finds out that historical events (up to some detail) can be theoretically modelled using equations, and then spends years trying to put the theory in practice. The new science of psychohistory founded upon his success can simulate history and extrapolate the present into the future.