Deuteronomy 13

Sugya Map: Bal Tosif and the False Prophet

• Issue: The intersection of Bal Tosif (Deut. 13:1) and the prohibition against following a Navi Sheker (false prophet) who performs signs.
• Nafka Mina: Is the prohibition of Bal Tosif merely about ritual precision, or does it delineate the epistemic boundary of the Torah?
• Primary Sources: Deut. 13:1–6; Sifrei Devarim 82; Sanhedrin 90a; Rambam, Hilkhot Yesodei HaTorah 9.1.

Text Snapshot

• Deuteronomy 13:1: "Be careful to observe only that which I enjoin upon you: neither add to it nor take away from it."
• Nuance: The Masoretic framing of Hashmer (be careful) as a lav (prohibition) is pivotal. Rashi (ad loc.) notes that while it functions as a lav, it carries no malkot (lashes) because it is a "prohibition derived from a positive command" (lav ha-ba miklal aseh).

Readings

• Sforno (13:1): Posits that Bal Tosif acts as a safeguard against human hubris. Even if one intends to "honor" God—such as burning children—adding to the Torah is inherently "despicable" because we lack the authority to validate innovations.
• Ha’amek Davar (13:1): Radically links Bal Tosif to the Torah She-be'al Peh. He argues that one cannot observe the Torah She-bi-khtav without the oral tradition; thus, "the word" (ha-davar) refers to the organic necessity of the Oral Law, framing Bal Tosif as a mandate to maintain the integrity of the total system.

Friction

• Kushya: If Bal Tosif forbids adding, how can the Sages enact gezeirot (rabbinic decrees)?
• Terutz: Rambam (Hilkhot Mamrim 2.9) clarifies that Bal Tosif only applies when one claims their addition is de-Oraita (Torah-level). Rabbinic enactments are recognized as distinct, protective fences (gezeirot), not as part of the immutable text itself.

Intertext

• Sanhedrin 90a: Explicitly debates the status of a prophet who commands a mitzvah temporarily (hora'at sha'ah). The prohibition of Bal Tosif is the very mechanism that invalidates a prophet who suggests an "addition" to the covenant, regardless of their miraculous portents.

Psak/Practice

The prohibition serves as a meta-halakhic heuristic: The Torah is a closed system. In practice, this means we do not innovate new mitzvot under the guise of piety. We revere the established boundary, recognizing that "observing" (tishmeru) is the primary mode of Jewish religious engagement, not augmentation.

Takeaway

Bal Tosif is not just about ritual mechanics; it is the ontological boundary of the Covenant. If the Torah is the "word" of God, any human "addition" is not a supplement, but a subversion.