Bal Tosif — The Prohibition of Adding On to the Torah
לֹא תֹסִפוּ עַל הַדָּבָר אֲשֶׁר אָנֹכִי מְצַוֶּה אֶתְכֶם
You shall not add to the word that I command you (Devarim 4:2)
Our parsha introduces us to the prohibition of Bal Tosif — of adding on to mitzvot. It is interesting to note that this mitzvah is perhaps unique among the mitzvot in that it receives no mention at all in the first four Chumashim, but then is mentioned twice in Chumash Devarim, both here and in Parshat Re’eh (13:1).
Also noteworthy is the fact that Chazal, in the Sifrei, chose to discuss the parameters of Bal Tosif in their comments on the pasuk in Re’eh, and not on our pasuk, even though it appears earlier in the Torah. The explanation commonly given for this is that Parshat Re’eh is already dealing with the halachic part of Chumash Devarim, which begins in Perek 13, while our pasuk is still in the section of Tochachah (Rebuke) which Moshe is administering to B’nei Yisrael.
However, if we look carefully at these two pesukim, both in terms of their phraseology as well as the context in which they appear, we will see that we are not dealing here with “Mishneh Torah” (repetition of a mitzvah) within Mishneh Torah (Chumash Devarim). Rather, these two pesukim represent two very different aspects within Bal Tosif.
Adding a Detail to a Mitzvah and Adding a Mitzvah to Taryag
The definition of Bal Tosif as found in Chazal (Sifrei, ibid.) and quoted in Rashi is that it comes to forbid an internal addition to a mitzvah, i.e. to add on a detail to a particular mitzvah, such as having five compartments for the tefillin. Elsewhere, Chazal discuss other ways of “adding on to a mitzvah,” such as extending the time for that mitzvah e.g. sleeping in a sukkah on Shemini Atzeret.
However, the Ramban, in his peirush to our pasuk, suggests an additional way of understanding this prohibition:
In my opinion, even if one decided to fabricate something as an independent mitzvah, for example, if he introduced a new chag in a different month to the Chagim of the Torah, as did Yeravam, he has violated this prohibition.
The Ramban has opened an entirely new avenue of understanding Bal Tosif, not as adding a detail to a specific mitzvah, but adding a mitzvah onto Taryag. We note that the Ramban presents this idea as his own opinion, for as we mentioned above, Chazal only discussed Bal Tosif in terms of adding a detail to a mitzvah. Nonetheless, Ramban feels that adding a mitzvah is also part of the prohibition. We might add, Ramban’s suggestion would seem to be supported by a kal vachomer. If adding on a particular detail to mitzvah is already a violation of Bal Tosif — even though the body of “Taryag Mitzvot” remains the same — then how much more so if a person seeks to introduce an entirely new mitzvah!
The Vilna Gaon: Two Parshiyot within Bal Tosif
The Vilna Gaon illuminates the entire sugya of Bal Tosif by demonstrating how the two types of Bal Tosif [adding a detail to a mitzvah and adding a mitzvah to Taryag] are reflected in the two places in the Torah where the prohibition is mentioned.
The pasuk in Re’eh (13:1) states:
אֵת כָּל הַדָּבָר אֲשֶׁר אָנֹכִי מְצַוֶּה אֶתְכֶם אֹתוֹ תִשְׁמְרוּ לַעֲשׂוֹת לֹא תֹסֵף עָלָיו
The entire word that I command you, that shall you observe to do, you shall not add to it.
Commenting on this pasuk, the Gaon writes (Aderet Eliyahu, Devarim, ibid.):
This refers to adding on a detail to the mitzvah itself, for example (adding a fifth species on to) a lulav-bundle, or to tzitzit, by having more than four sets of strings. It is from this pasuk that Chazal (Zevachim 80a) derived the prohibition against adding an application of blood (on the Mizbeach) to a korban that requires four, or to a korban that requires (only) one.
With regards to the pasuk in Parshat Va’Etchanan which also forbids adding on to mitzvot, that pasuk is expounded as forbidding adding (a mitzvah) on to the Taryag Mitzvot. For in the beginning (of that pasuk) it says, “שְׁמַע אֶל הַחֻקִּים וְאֶל הַמִּשְׁפָּטִים אֲשֶׁר אָנֹכִי מְלַמֵּד אֶתְכֶם לַעֲשׂוֹת — Heed the statutes and laws that I am commanding you to do,” and in that regard it proceeds to state “לֹא תֹסִפוּ עַל הַדָּבָר אֲשֶׁר אָנֹכִי מְצַוֶּה אֶתְכֶם — You shall not add on to the matter that I am commanding you.” In this Parsha, it refers to “כָּל הַדָּבָר — the entire matter,” and thus it is here that Chazal expounded that one may not add anything on to the mitzvah itself.
This is pshuto shel mikra at its finest! The very same words are understood as referring to two separate types of Bal Tosif, the parameters of which are derived, not from the words themselves, but from the context in which they were written.
Rav Betzalel HaKohen
The distinction between the two mentions of Bal Tosif in the Torah is developed by another Torah luminary of Vilna, Rav Betzalel HaKohen, in the generation after the Vilna Gaon. In his She’eilot U’Teshuvot Reishit Bikkurim (siman 7), he writes:
It appears to me that in truth we need to explain why the prohibition of Bal Tosif is written in Parshat Va’Etchanan in the plural (“לֹא תֹסִפוּ”), while in Parshat Re’eh it is repeated, but written in the singular (“לֹא תֹסֵף”).
Therefore, it appears that both pesukim are necessary, for there are two types of Bal Tosif. The pasuk in Va’Etchanan, which was stated in the plural, clearly refers to those who wish to add a mitzvah to Taryag, something which is only really applicable to the Beit Din HaGadol who seeks to introduce a new mitzvah that would be obligatory for all Am Yisrael. It is with regard to this that the pasuk states, “לֹא תֹסִפוּ” in the plural, for this prohibition applies to the group of people who make up the Sanhedrin.
In contrast, when the Torah repeats this prohibition in Parshat Re’eh, it does so using the singular form, for this clearly refers to any individual who seeks to add a detail on to a mitzvah beyond that which is either written in the Torah, or known to us through a kabbalah (tradition) of Torah Shebaal Peh. For example, one who adds a berachah to birkat Kohanim which was not specified in the Torah, or adds a fifth species to the lulav-bundle, or a fifth compartment to the tefillin. It is regarding this type of addition that each individual is told “לֹא תֹסֵף,” in the singular.
It is for this reason the drashah of Chazal regarding adding on to lulav, tzitzit, and Birkat Kohanim was only mentioned in Parshat Re’eh, not [earlier] in Parshat Va’Etchanan. This similarly explains why the Rambam and all others who codified the mitzvot quoted the pasuk in Parshat Re’eh as the source for the prohibition of Bal Tosif, and not the earlier pasuk in Parshat Va’Etchanan. For these mefarshim were discussing the prohibition against adding on a detail to the mitzvah itself, therefore they quoted the pasuk in Re’eh which is written in the singular form and addresses the individual.
The very same distinction arrived at by the Vilna Gaon through paying attention to the context of the two prohibitions is arrived at by Rav Betzalel by noting the grammatical form of the prohibitions themselves! We should add that it is clear that Rav Betzalel does not mean to say that the first type of Bal Tosif (adding a mitzvah) applies only to the Sanhedrin, while the second type (adding a detail) applies only to the individual. Rather, it is through phrasing the prohibitions in terms of who might typically come to violate them (דיבר הכתוב בהוה), the Torah allows us to understand the type of Bal Tosif that it is referring to. Adding a new mitzvah would typically be a concern regarding the Sanhedrin, while adding a detail would typically be a concern regarding the individual performing the mitzvah.
 See e.g. Rosh Hashanah 28b.
 See Melachim I, 12:33.
 Actually, although this second type of Bal Tosif is not referred to by Chazal in the Gemara or collections of midrash halachah, it is found in the Midrash Pesikta Zutrata to this pasuk: “You shall not add on to the mitzvah that I am commanding you … for example, the festival that Yeravam invented in the month that he fabricated from his heart.”
 [I.e., the matter of keeping all the mitzvot, mentioned in the beginning of the pasuk.].
 I.e. Parshat Re’eh where Bal Tosif is mentioned a second time.