A prediction is a statement or claim that a particular event will occur in the future in more certain terms than a forecast. The etymology of this word is Latin (from præ- "before" plus dicere "to say"). Niels Bohr stated "Prediction is very difficult, especially if it's about the future."

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Informal prediction from hypothesis

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 sound reasoning and accurate data. Large corporations invest heavily in this kind of activity to help focus attention on possible events, risks and business opportunities, using futurists. Such work brings together all available past and current data, as a basis on which to develop reasonable expectations about the future.

Opinion Polls

In politics it is common to attempt to predict the outcome of elections via Political Forecasting techniques (or assess the popularity of politicians) through the use of opinion polls. Prediction games have been used by many corporations and governments to learn about the most likely outcome of future events with amazing accuracy.

Supernatural (prophecy)

Predictions have often been made, from antiquity until the present, by resorting to paranormal or supernatural means, such as prophecy or by observing omens. Disciplines including water divining, astrology, numerology, and fortune telling, along with many other forms of divination, have been used for centuries or even millennia to predict or attempt to predict the future. So far none of these means of prediction have been proven under controlled conditions and are heavily criticised by scientists and skeptics.

Anticipatory science forecasts

In a scientific context, a prediction is a rigorous, (often quantitative), statement forecasting 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 assertions which are logical consequences of scientific theories. This is done through repeatable experiments or observational studies.

A scientific theory whose assertions are not in accordance with observations and evidence will probably be rejected. Theories that make no testable predictions remain protosciences until testable predictions become known to the community.

Additionally, if new theories generate many new predictions, they are often highly valued, for they can be quickly and easily confirmed or falsified (see predictive power). In many scientific fields, desirable theories are those which predict a large number of events from relatively few underlying principles.