Scientific thought aims to make correct predictions about events in nature. Although the predictive nature of scientific thought may not at first always be apparent, a little reflection usually reveals the predictive nature of any scientific activity. Just as the engineer who designs a bridge ensures that it will withstand the forces of nature, so the scientist considers the ability of any new scientific model to hold up under scientific scrutiny as new scientific data become available.

It is often said that the scientist attempts to understand nature. Ultimately, understanding something means being able to predict its behavior. Scientists, therefore, usually agree that events are not understandable unless they are predictable. Although the word "science" describes many activities, the notion of prediction or predictability is always implied when the word is used.

Until the seventeenth century, scientific prediction simply amounted to observing the changing events of...