Belief in demons, though not very pronounced in Jewish life and thought, is still prevalent, in a semi-comical way, at the level of folklore. Even some of the learned feel compelled to accept, perhaps not too seriously, belief in demons because this belief is implied in the Talmud in many places.
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Needless to say, sophisticated Jewish thinkers who did believe in the existence of demons did not think of these as little devils with forked tails breathing fire but as spiritual forces which God has unleashed in the world for purposes of His own, or as harmful psychological processes which take place in the human mind.