Deuteronomy 13

Sugya Map

• Core Issue: The epistemological and halakhic boundaries of the Mitzvah system. Does the prohibition of Bal Tosif (Do Not Add) and Bal Tigra (Do Not Subtract) apply to the meta-structure of the Law, or merely the granular performance of specific commandments?
• Nafka Mina:
  • Can a prophet override a standing mitzvah via a "sign"?
  • Does a monarch have the authority to rationalize away a commandment based on his own perceived immunity to its potential negative outcomes (the Solomonic problem)?
  • The status of Torah She-be'al Peh (Oral Law) as an essential component of the "Word" (ha-davar) mentioned in Deuteronomy 13:1.
• Primary Sources:
  • Deuteronomy 13:1–6 (The Prophet/Diviner).
  • Sifrei Devarim 82 (Source of the prohibition).
  • Rambam, Hilkhot Mamrim 2:9 (Definition of Bal Tosif).
  • Sanhedrin 90a (The status of the "True Sign" of the false prophet).

Text Snapshot

• Deuteronomy 13:1: "אֵת כָּל-הַדָּבָר אֲשֶׁר אָנֹכִי מְצַוֶּה אֶתְכֶם אֹתוֹ תִשְׁמְרוּ לַעֲשׂוֹת לֹא-תֹסֵף עָלָיו וְלֹא תִגְרַע מִמֶּנּוּ."
• Nuance: Note the definite article in "הַדָּבָר" (the Word/the Thing). The Haamek Davar (ad loc.) argues this is not a general reference, but a specific synecdoche for the Torah She-be'al Peh. The dikduk here suggests that the davar is a singular, unified entity. If you sever the Oral transmission from the Written, you are not merely failing to perform a mitzvah; you are violating the integrity of the davar itself—the functional unit of divine instruction.

Readings

1. Sforno: The Rationalist’s Boundary

Sforno treats the prohibitions of Bal Tosif and Bal Tigra as guardrails against the "tyranny of the ego." His reading of Bal Tigra is particularly striking: he invokes the figure of King Solomon, who assumed he could bypass the restrictions on royal accumulation (Deut. 17:17) because his wisdom and righteousness made him immune to the ta'am (reason/rationale) behind the prohibition.

Sforno’s chiddush is that the Torah’s commands are not dependent on their ta'am. When one subtracts because "the reason no longer applies," one is effectively declaring oneself the author of the law. For Sforno, the Davar is absolute; the moment a human subject begins to curate the Law based on internal logic, they have exited the covenantal structure. This transforms Bal Tigra from a technical rule about mitzvah performance into a fundamental warning against secularizing the divine prerogative.

2. Haamek Davar: The Oral-Written Synthesis

The Netziv (Rabbi Naftali Zvi Yehuda Berlin) provides a more radical structural reading. He asserts that "the Word" (ha-davar) refers to the entirety of the Oral Law. He argues that it is logically impossible to perform the Written Law without the oral tradition.

His chiddush is that the prohibitions of Bal Tosif and Bal Tigra are the very mechanisms that mandate the existence of Torah She-be'al Peh. By commanding "Do not add or subtract," the Torah creates a closed system that can only be understood through the tradition that explains how to navigate the "light" and "grave" precepts. For the Netziv, the Mitzvah is not just the act; it is the system. Any attempt to interpret the text sola scriptura is, in his view, an act of Tigra (subtraction), as one is removing the essential interpretive layer that makes the davar actionable.

Friction

The Kushya: The Prophet’s Paradox

The most potent kushya arises from the juxtaposition of the "False Prophet" (Deut. 13:2-6) and the authority of the Prophet in general. If a prophet performs a miracle—a "sign or portent" that comes true—the Torah explicitly tells us to ignore them if they advocate for Avodah Zarah or attempt to change the davar.

But here is the friction: If the Torah is a closed system (as per Bal Tosif), how can we validate the prophet's "sign" without it becoming a form of "addition" to the revelation? The Gemara in Sanhedrin 90a struggles with this: if the sign is true, why is the prophet a deceiver?

The Terutz: The Test of Love

The Torah provides the answer in v. 4: "For the ETERNAL your God is testing you." This is not a logical contradiction; it is an ontological one. The terutz is that the "Sign" is irrelevant because the Davar has already been finalized at Sinai.

Rashi (on 13:4) clarifies that the test is designed to see if your love for God is predicated on the content of the command or the utility of the miracle. A true prophet is a messenger of the Davar; a false prophet, even one who performs miracles, is an agent of "another god" because they are attempting to introduce a new variable into a closed system. The mitzvah of Bal Tosif is the shield that allows the Jewish people to reject empirical evidence (the miracle) in favor of the finalized constitutional text (the Torah). You do not "add" a new revelation to the old one, even if the new one comes with fireworks.

Intertext

• Sanhedrin 90a: The Talmud discusses the "Prophet who prophesies in the name of Avodah Zarah." The sages argue that even if he performs a miracle, he is liable for death. This maps perfectly onto our text: the sign is not a source of authority. Authority resides only in the Davar that was given and sealed.
• Shulchan Aruch, Orach Chayim 589: The laws of Tashlumin (making up missed prayers). Here, the Sages have added a prayer structure, but it is not Bal Tosif. Why? Because the Davar includes the mandate to listen to the Sages (Deut. 17:11). This reinforces the Netziv’s point: the Oral Law is the "Word" that defines the boundaries of the Written.

Psak/Practice

In the contemporary context, this sugya serves as a meta-halakhic heuristic for "Innovation vs. Development."

1. Innovation (Addition): Any practice that claims to be a mitzvah but lacks a root in the Masorah (the transmission of the Davar) is a violation of Bal Tosif.
2. Rationalization (Subtraction): Any attempt to nullify a mitzvah based on the claim that its "context" or "historical necessity" has changed (the Solomonic error) is a violation of Bal Tigra.

Meta-Psak: The Davar is a closed loop. We do not look for new "signs" or "rationales" to validate the Law; we look to the internal mechanics of the Torah She-be'al Peh to understand its application.

Takeaway

The prohibition against adding or subtracting is the Torah’s "seal." It protects the integrity of the Davar against both the charismatic prophet who offers new revelations and the sophisticated intellectual who offers new rationalizations.