Rudolf Steiner

By giving material expression to force-forms in space, the Greeks gave divine spiritual beings the opportunity of using these material forms. It is no figure of speech but a fact when we say that gods came down at that time into the Greek temples in order to be among human beings on the physical plane.

Observation and thinking are the two points of departure for all the spiritual striving of man, insofar as he is conscious of such striving. The workings of common sense, as well as the most complicated scientific researches, rest on these two fundamental pillars of our spirit.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.