Prediction, SF Encyclopedia, David Langford and Peter Nicholls.
The most widespread false belief about sf among the general public is that it is a literature of prediction. Very few sf writers have ever claimed this to be the case, although Hugo Gernsback did see one function of his sf magazines as to paint an accurate picture of the future. Very few of the stories he published lived up to his editorializing. When John W Campbell Jr took over the editorship of Astounding he demanded an increasing scientific plausibility from his writers, but a plausible-sounding “perhaps” is a long way from prediction.