I've tried for the better part of the morning to put together a post explaining the official DovBear view on Judaism and the supernatural. It hasn't been easy. Not because I'm unsure of my opinion, but because it's such an unwieldy topic. Judaism and the supernatural is a book, not a blog. So, long story short: I don't believe in anything, unless Jewish law demands it.
Here's the break down:
Magic, fortune-telling, astrology and similar
Don't believe in any of it. (1) and (2)
Ghosts and Demons
Don't believe in them. See the Rambam:
Commentary to Mishna Avoda Zara 4, 7.
Hilchot Avoda Zara 11: 11, 16.
Morah: 3, 46.
Miracles
If they're reported in the Torah, I believe that they are true, but you need to remember that "true" is a slippery word. We can both, for example, say "Kriyat Yam Suf" is a "true" story but have in our minds very different ideas about what actually happened. If they aren't reported in the Torah, they aren't miracles, but magic, and magic isn't real.
Loose ends
Ok, those of you who haven't stormed off muttering "apikorus" probably have follow up questions. We'll deal with them in the comments.
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(1) Rambam, Yad Hachazaka: [Belief in] astrology, sorcery, oaths, lucky charms, demons, forecasting the future, and talking to the dead - all these are the essence of idol worship, and are lies that fools believe to be both true and wise, or were lies made up by the rulers to cheat the public. All these things are based on false beliefs, which have no point or use. He who believes that these are true practices -but forbidden by the Torah- is nothing but a fool. . . . the only person who will use these beliefs is one who is a gullible person who will believe anything, or a fraud who wishes to cheat the public."
(1a) Rambam, Yad Hachazaka: And these things [ie: magic, witchcraft, sorcery, and superstition] are all lies and deception... it isn't proper for Jews, who are wise and clever, to continue this nonsense and it should never enter their minds that there is an advantage or benefit [to'elet] to using these things... any person who believes in these things and imagines that there is truth and wisdom behind them - though the Torah prohibits them (to Jews) - is from among the fools and the stupid people [scholim u'chasrei daa't] and in the category of [people] who have incomplete mental facilities. Those who posses authentic wisdom and pure knowledge know through clear proofs that every one of these things that the Torah prohibited is not wisdom, but nothingness and nonsense [tohu v'hevel] that is continued by empty-headed people [chasrei da'at] who have caused the ways of truth to be abandoned.
(2) Ibn Ezra (Leviticus, 19:31):"Those with empty brains say 'were it not that fortune tellers and magicians were true, the Torah would not prohibit them.' But I (Ibn Ezra) say just the opposite of their words, because the Torah doesn't prohibit that which is true, but it prohibits that which is false. "