This mitzvah prohibits doresh el hameitim — consulting or summoning the dead for guidance. Rambam describes necromancy as fasting in cemeteries, chanting incantations, or performing rituals to receive dreams or messages from the dead (Hilchot Avodat Kochavim 11:13). The Talmud (Sanhedrin 65b–66a) expands on this, identifying practices such as raising voices from bones, grave-sleeping, and conjuring spirits. Rashi (Deut. 18:11) explains it as one who fasts and lodges among graves so that a dead person appears to him in a dream. Ramban insists that Israel must reject such practices because Torah provides prophecy as the true channel of divine guidance, not necromancy. Sefer HaChinuch (Mitzvah 512) teaches that necromancy is deception that corrupts faith, as the dead cannot speak; those who claim such powers mislead the living. Midrash Tanchuma (Shoftim 8) contrasts Israel with the nations: while they chase after the dead, Israel seeks Hashem, the Living G-d.

Commentary & Classical Explanation:

• Rambam (Hilchot Avodat Kochavim 11:13; Sefer HaMitzvot, Lo Ta’aseh 34): Defines necromancy as rituals intended to summon the dead for knowledge.
• Talmud (Sanhedrin 65b–66a): Lists necromantic practices, including conjuring spirits through bones or graves.
• Rashi (Deut. 18:11): Describes necromancers fasting in cemeteries to induce dreams of the dead.
• Ramban (Deut. 18:9): Teaches that Torah directs Israel to prophecy and Hashem, not necromantic rites.
• Sefer HaChinuch (Mitzvah 512): Explains the prohibition protects Israel from deception and false hope in necromantic claims.
• Midrash Tanchuma (Shoftim 8): Contrasts nations who seek the dead with Israel, who seeks the Living G-d.

Contrast with Mitzvah 63 (Not to Mutter Incantations):

• Both involve forbidden speech. Incantations manipulate nature through chants, necromancy seeks guidance from spirits.
• Rambam (Hilchot Avodat Kochavim 11:12–13): Incantations are illusions; necromancy is more severe, directing dependence toward the dead instead of Hashem.

Parallel to Prophecy (Mitzvah 9):

• Ramban (Deut. 18:15) highlights prophecy as Israel’s true form of guidance, given in place of foreign necromantic practices.
• Talmud (Sanhedrin 90a) affirms “ein doresh el hameitim” — prophecy and Torah, not spirits, are Israel’s lifeline to Hashem.

Contrast with Jewish Memorial Practices (Yizkor and Kaddish):

• Rambam (Hilchot Avel 13:1) and Shulchan Aruch (Yoreh De’ah 376) affirm the proper way to honor the dead is through mitzvot — charity, prayer, and Torah study — not communication.
• Talmud (Shabbat 152b): “The righteous, even in death, are called alive” — meaning their merit continues through the deeds of the living.
• Sefer HaChinuch (Mitzvah 403): Teaches that mitzvot in the physical realm uplift the spiritual, showing the Torah’s channel for honoring the dead without necromancy.