John Boyd Science fiction is story-telling, usually imaginative as distinct from realistic fiction, which poses the effects of current or extrapolated scientific discoveries, or a single discovery, on the behavior of individuals of society. Mainstream fiction gives imaginative reality to probable events within a framework of the historical past or present; science fiction gives reality to possible events, usually in the future, extrapolated from present scientific knowledge or existing cultural and social trends. Both genres ordinarily observe the unities and adhere to a cause-and-effect schema.