noun
BAD : Were the voices real or just products of his fantasy?
GOOD : Were the voices real or just products of his imagination?
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fantasy = a picture in the mind produced by the imagination, especially one which is very different from reality: 'He lived in a world of fantasy.'
imagination = (the part of the mind with) the ability to produce mental pictures: 'Unlike adults, young children are usually full of imagination.' 'His paintings show great technical skill but a lack of imagination.'