Defining Science Fiction

George Hay ("futurologist")    
Brian Aldiss (science fiction writer)    
H. G. Wells (polymath)    
Eric Rabkin (tri-partite definition)    
Frederic Brown (science fiction writer)    
Eric Rabkin (theoretical definition)    

Eric Rabkin:

That branch of the fantastic that makes its narrative world plausible against a background of science.

  robot-thinker