    Senfenee 1: It has been suggested thal SF include only those  slories which would be invalidated without their scientific  content; that fietion which concerns science, scientists, and the  impact of science on humans: thal which explores allernate  existences (whether future, extraterrestrial, or only in  characlers' minds) based on facts and logieal progression via  scientific method.    Sentence 2: Everyone agrees that SF stories ean ignore facts  and logic.