The Gemara in Berakhot 6a:2-4 speaks of demons as a real, pervasive population surrounding human beings — thousands to each side — whose presence would overwhelm a person if the eye could perceive them, invoking Tehillim 91:7 as the verse that shields man from this unseen multitude.
Chagigah 16a:5-7 gives demons a defined ontological status partway between angels and humans: like angels they have wings, traverse the world instantly, and overhear the future from behind the heavenly curtain, yet like humans they eat, reproduce, and die — a hybrid nature rather than mere metaphor.
Several aggadic passages trace demonic origins to specific historical events: Sanhedrin 109a:5 attributes the creation of demons and female demons to the generation that built the Tower of Bavel to wage war in heaven, while Eruvin 18b:10-12 records that Adam himself, during the years he was under ostracism following the sin of the Tree of Knowledge, fathered spirits, demons, and female demons, drawing this from the gap in Bereishit 5:3 before he begot a son in his own image.
The Torah and Nevi'im themselves use the term shedim for the objects of idolatrous sacrifice, as in Devarim 32:17 and Tehillim 106:37, and Yeshayahu 13:21 describes se'irim dancing in a desolate ruin, a verse that Rashi (Devarim 32:17) links lexically to se'irim as demons in his second explanation of the word שערום, showing that the rabbinic conception has roots in the pesukim themselves; the Ramban (Devarim 32:17) notes only that he has already explained this term elsewhere.
Halachic and philosophical sources treat demons as functioning agents within creation rather than mere folklore: Sanhedrin 65a:17-18 discusses one who burns incense to a demon as a capital offense tied to idolatry, Sanhedrin 65b:14-15 describes necromancy as a spirit of impurity settling on a person who starves himself in a graveyard, and Pesachim 110a-112b and Gittin 68b-69a narrate direct interactions between Sages like Rav Yosef and Shlomo HaMelech with named demons such as Yosef Sheida and Ashmedai, king of the demons.
Later mystical and philosophical works develop the nature of demons further: Nefesh HaChayim, Gate III 12:1-3 ties sorcery and the demonic realm to the powers of the impure Merkavah which the Sanhedrin needed to know in order to judge such cases, Recanati on the Torah, Achrei Mot:20 cites rabbinic sources suggesting demons have no physical body at all but are forces emanating from the attribute of judgment, and Gur Aryeh on Bamidbar 23:22 explains that demons partake of both earthly and heavenly qualities, reaching from the ground to the sky. Sulam on Zohar, Pinchas 763 further distinguishes between Jewish demons bound to the name Shaddai and demons of impurity associated with idolatry, while Tanya, Part I; Likkutei Amarim 24:3-5 frames the kelipah and its evil emissaries as fully subordinate to God's will, unable to act except by His commission.
Bereishit 6:1-4 and Rashi (Bereishit 6:19), who reads 'all living things' brought into the ark as including demons, extend the scope of these beings into the primordial narrative, while Midrash Tanchuma, Vayeshev 4:1 parallels this by describing the angel of death as fashioned on the first day of creation, showing that non-human spiritual agents are woven into the earliest layers of creation accounts.
Sefer HaIkkarim, Maamar 4 30:3-4 argues on philosophical grounds that since God's creation is maximally complete, every logically possible category of being must exist, including intermediate classes between corporeal and incorporeal existence, which supports a framework in which non-physical rational beings such as angels and demons are not merely imaginative but ontologically necessary.
Halachic codifiers treat engagement with demons as forbidden rather than theoretical: Shulchan Arukh, Yoreh De'ah 179:16 prohibits demonic practices while recording a dissenting view permitting inquiry of demons about stolen property, and the Rema adds that forcing them to swear by Divine Names is permitted by some, though most who engage in this do not escape unharmed; Shulchan Arukh, Yoreh De'ah 116:1-2 separately notes that uncovered liquids were forbidden by the Sages out of concern that a snake drank from them, a concern no longer operative since snakes are not common among us; and Shabbat 67b:1 discusses an incantation invoking 'Gad' as partaking of the ways of the Amorite, which Rabbi Yehuda identifies as a name of idolatry.
Among later readers of these sugyot, Valle on Bereishis 6 explains that certain shedim could coexist peacefully with humans and even entered the ark in companionship, despite their generally hostile nature, and Chiddushei Aggadot, Sanhedrin 65 distinguishes a righteous person who may receive a spirit of purity and closeness to God from sorcerers and magicians who operate through demons; Chiddushei Aggadot, Gittin 68 further contrasts angels appointed to sustain the world's governance with shedim, who damage and harm it.
A modern treatment, Rav Eliezer Melamed (Peninei Halakhah, Women's Prayer 5:3), records a competing view among later authorities that the ru'ach ra'ah discussed in the Talmud has effectively ceased to operate in later generations and in other lands, citing Tosafot, the Lechem Mishneh on the Rambam, and the Maharshal, alongside the understanding that spiritual and mystical forces were more pronounced in earlier generations than today.
Be'er Moshe (Be'er Moshe 5:1) addresses creatures associated with a 'bad spirit' found in the synagogue, directing the reader to further discussions of the matter in other cited works.
Igros Moshe (Igros Moshe YD 4:13) draws a distinction between supernatural phenomena produced through sorcery that involves impure names and demons, and other supernatural matters that involve ordinary words and actions unrelated to sorcery.
Tzitz Eliezer (Tzitz Eliezer 13:55) cites a Gemara in Avodah Zarah regarding suffering sent upon a person being adjured not to pass through a particular person or by means of a particular substance.