On our daf, we are told an incredible idea about the letters in the aleph bet (alphabet)
The 5 letters that change form at the end of a word (מנפצך) were not always like that!
The open form of the letters used at the beginning and in the middle of words were actually a newer innovation of the נביאים prophets! (Rashi points out that in a parallel sugya (Megillah 2b), the claim is that the closed form at the end of the word was the later addition- see there for how he resolves this.)
It is the closed form of the letters that we only use at the end which were actually the original, and the prophets for some reason introduced the open form everywhere except at the end of the word!
The Gemara takes major issue with this statement, calling on the passuk ” אלה המצוות” (“THESE are the laws” – Devarim 36/13 )which teaches us that only the commandments given to Moshe at Sinai were valid and from then on, no prophet could innovate anything else- אין הנביא רשאי לחדש דבר .
The Gemara replies that both forms actually existed already, the prophets simply decided which form to use at the end of the word and which form to use in the rest of the world.
That too is rejected, seeing as even such a decision would be considered an innovation, which prophets may not make.
The Gemara finally concludes that both forms of the letter as well as where they were to be used were indeed given over to Moshe, but they were forgotten, and the Nevi’im (prophets) reestablished them.
In a different sugya, even the reading of the Megila , a Mitzva instituted by the prophets Mordechai and Esther, was subject to scrutiny by Chazal (Megila 14a) , and they pointed out that none of the Nevi’im added to anything in the Torah except in this case, due to a קל וחומר (fortiori logical argument) that they found.
From our daf, however, we see that this rule doesn’t only apply to introducing new Mitzvos, but also applies to changing the form of the Hebrew letters, or even deciding when each form should be used!
As similar concept is found in the beginning of Bava Kama (2b) , where the Gemara tries to derive that נגיחה (goring) must be done with the horns of an ox to be considered נגיחה , from a Passuk in Navi (Melachim I 22/11.)
The wicked king of Israel, Achav, has convinced the righteous king of Yehuda, Yehoshafat, to go to war with Aram to claim back Ramot Gilad, which they had occupied.
All the false and/or idolatrous prophets tell Achav exactly what he wants to hear, namely that he will succeed, but Yehoshafat insists that he look for a surviving true prophet of Hashem from whom to seek council.
Meanwhile, one of these “yes men”, Tzidkiya ben Kenaanah, takes two large metal horns and told Achav and the people that they would use these horns to “gore” the enemy into submission
The true navi, Michayahu, in contrast, predicts that the war will be a disaster and advice them to stay home.
For this, he is imprisoned by Achav’s men, and the two kings lead their troops into battle together.
(We see similar treatment of our great prophets who refuse to give people the false sense of comfort that they want and speak truth to power, in many places in Tanach, one of the most famous being the horrendous incarceration of Yirmiyah but the last king of Yehuda, Tzidkiya, for similarly breaking ranks with all the false prophets and advising surrender to the approaching Babylonians.)
Back to the horns of Tzidkiya, Chazal derive from here that the word יגח ( yigach), refers to injuring with the horns.
However, another source from the Chumash is also given for this, and the Gemara explains that this is because one might counter that דברי תורה מדברי קבלה לא ילפינן – one may not derive words of the Torah from the words of Kabbalah (the term used by Chazal for prophecy, but that’s another discussion!)
In the end, the Gemara still accepts this proof, seeing as we are not deriving any laws per se, but simple learning the meaning of a word (גלוי מלתא) which is acceptable.
Here, we were not attempting to derive new mitzvas from the Neviim, but simply some details of the laws mentioned in the Torah through a גזירה שוה ( Masoretic comparison based on similar language) – namely that the damages that the Torah is referring to need to be by the horns of the ox ,in order for the relevant laws to apply.
Yet even this is not considered valid, and the only thing that we can actually apply from the words of the Nevi’im to Torah matters is shedding light on the meaning of words used in the Torah- this is not through a גזירה שוה but simply a גלוי מילתא.
However, it does not take much to see that this cannot be so straight forward as it looks.
So many new laws of Shabbos, including the mitzvas of honoring and enjoying shabbos (כבוד ועונג שבת ) as well as the prohibition of עובדין דחול ( weekday activities that are not melacha but inappropriate for shabbos) are derived from the famous speech of Yeshayahu, which we read as the haftarah from Yom Kippur (Yeshayahu 58/13.)
In addition, Chazal tell us )Shabbos 24b) that Shlomo haMelech instituted נטילת ידים (washing hand before eating bread)and Eruvin, mentions many decrees made by various biblical figures, and of course, made so made so many decrees of their own!
Even the Mitzva of Chanukah, instituted by Chazal long after the period of prophecy, is accepted, due to the biblical injunction to follow the Torah leadership and prohibition against going against it (Shabbos 23a).
Why could the same not apply to a relatively simple matter of the shape of the letters, or learning how נגיחה is done?
Perhaps the key lies in the famous words of the Rambam (Mamrim 2/9), where he asks how it is possible for Chazal to make decrees against things the Torah does not forbid, when there is a prohibition to add or subtract from the Torah.
He notes that the prohibition of adding to the Torah applies to making new laws and making out as if they are biblical laws.
However, so long as they are clear that they are rabbinical laws, there is no issue, and on the contrary, it is part of their mandate (probably from the passuk לא תסור and ושמרתם את משמרתי.)
The same argument might be applicable not only to the decrees the Rambam mentions, but also to entirely new rabbinical mitzvas, though one would want to explain why the Rambam fails to mention this.
The case we see on our daf is not a new rabbinical mitzva or decree, but an actual change in the biblical laws as to how to write a sefer-Torah and other holy scrolls.
Similarly, the case in Bava Kama is not a new rabbinical form of liability for damages, but a derivation by גזירה שוה of the details of biblical laws, from verses in the prophets.
In truth though, even without having thoroughly examined each sugya where the idea of אין נביא רשאי לחדש דבר is mentione, I see a major issue with using this approach- the case of Megillah has no pretensions of being a biblical Mitzva, but is a מצוה מדברי סופרים ( a commandment initiated by the prophets or sages.)
If so, why was a קל וחומר argument needed in order for Mordechai and Esther to initiate it?
Surely it should have been permitted without such an argument for the same reason as Chanukah was!