Uncertainty

There are many situations in which we do not know precisely what will happen.

Examples

In each situation, it could be argued that the outcome is largely deterministic — for example, if we knew exactly the temperatures and air pressures around the globe at present, understood the mechanics of changing weather and had enough computing power, we should be able to get an extremely accurate forecast of the midday weather tomorrow. However with current knowledge, there is no choice but to treat the outcome as being random, with various possible outcomes.

Probability

Uncertainty is described by the probabilities of the different possible events that might occur. We will properly describe how probability might be defined later in this section, but the concept is that its value describes chance on a scale of zero to one, as shown below.