It has been suggested that SF include only those stories which would be invalidated without their scientific content;  that fiction which concerns science, scientists, and the impact of science on humans;  that which explores alternate existences (whether future, extraterrestrial, or only in characters' minds) based on facts and logical progression via scientific method.
( It ( ( has ( been ( suggested ( that ( SF ( include ( ( ( ( ( ( ( ( only ( those stories ) ) ( which ( would ( be ( invalidated ( without ( their ( scientific content ) ) ) ) ) ) ) ) ; ) ( ( that fiction ) ( which ( ( concerns ( ( ( ( ( science , ) scientists ) , ) and ) ( ( the impact ) ( of science ) ) ) ) ( on humans ) ) ) ) ) ; ) ( that ( which ( ( ( explores ( alternate existences ) ) ( -LRB- ( ( ( ( ( ( ( whether future ) , ) extraterrestrial ) , ) or ) ( only ( in ( ( characters ' ) minds ) ) ) ) -RRB- ) ) ) ( based ( on facts ) ) ) ) ) ) and ) ( ( logical progression ) ( via ( scientific method ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ has) (VP (VBN been) (VP (VBN suggested) (SBAR (IN that) (S (NP (NNP SF)) (VP (VBP include) (NP (NP (NP (RB only) (DT those) (NNS stories)) (SBAR (WHNP (WDT which)) (S (VP (MD would) (VP (VB be) (VP (VBN invalidated) (PP (IN without) (NP (PRP$ their) (JJ scientific) (NN content))))))))) (: ;) (NP (NP (DT that) (NN fiction)) (SBAR (WHNP (WDT which)) (S (VP (VBZ concerns) (NP (NP (NN science)) (, ,) (NP (NNS scientists)) (, ,) (CC and) (NP (NP (DT the) (NN impact)) (PP (IN of) (NP (NN science))))) (PP (IN on) (NP (NNS humans))))))) (: ;) (NP (NP (DT that)) (SBAR (WHNP (WDT which)) (S (VP (VBZ explores) (NP (JJ alternate) (NNS existences)) (PRN (-LRB- -LRB-) (NP (NP (IN whether) (JJ future)) (, ,) (NP (JJ extraterrestrial)) (, ,) (CC or) (NP (NP (JJ only)) (PP (IN in) (NP (NP (NNS characters) (POS ')) (NNS minds))))) (-RRB- -RRB-)) (PP (VBN based) (PP (IN on) (NP (NNS facts)))))))) (CC and) (NP (NP (JJ logical) (NN progression)) (PP (IN via) (NP (JJ scientific) (NN method))))))))))) (. .)))
Many Science Fiction stories are wholly unscientific and should instead be categorized as Fantasy.
( ( Many ( Science ( Fiction stories ) ) ) ( ( ( ( are ( wholly unscientific ) ) and ) ( ( should instead ) ( be ( categorized ( as Fantasy ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Many) (NNP Science) (NNP Fiction) (NNS stories)) (VP (VP (VBP are) (ADJP (RB wholly) (JJ unscientific))) (CC and) (VP (MD should) (ADVP (RB instead)) (VP (VB be) (VP (VBN categorized) (PP (IN as) (NP (NNP Fantasy))))))) (. .)))