Imagination is about what is possible but didn't happen. Fantasy is about what is impossible.
My understanding: Imagination is about what is truthful though may not be factual. Fantacy is non-truthful and thus useless. Truly great poets possess true imagination, as in here, Allan Poe on cosmology. China's mighty poet 海子 has this capability in philosophy, history, anthropology, civilization etc. One who truly understands Hai Zi should understand what I am refering to here.
This type of insight usually presents itself in poetic form supported with sound logic.
