TORAH SHEBALPEH------agadita, authority of

The Gemora in Sanhedrin (100a) tells that R. Yochanan derived from a posuk that when Moshiach comes, the gates of Jerusalem will be made of jewels 30 amos long and 30 amos high. Some student said that such big jewels do not exist - "we do not even find jewels as big as dove's eggs," he said.

Then, one day the student saw angels (!) cutting such big stones, and he asked them what they are for. The angels answered: "They are for the gates of Jerusalem". When next he saw R. Yochanan, he praised his qualifications for expounding the Torah, based on his "scientific observation" that confirmed the Rebbi's interpretation.

R. Yochanan responded, "Bum! You only believe because of what you see? You dishonor the words of the sages!" and the student died.

The Ran (Drashos #13) points out that the statement of R. Yochanan had no halachic relevance at all - it was merely an Agadic interpretation, and the disagreement was regarding a scientific fact, yet the student was punished for not believing in its truth. Therefore, he concludes:

"Just as we are commanded to follow their opinions regarding laws of the Torah, so too are we commanded to follow all of what they say from tradition in Hashkafa ("Deos"), and medrash on Pesukim. And someone who veers from their words, even in something that has no relevance to any Mitzvah, is an Apikores and has no share in the next world.

The Radvaz (4:232) writes that "Aggadah is part of the Torah shebal peh and is rooted in what Moshe received on Har Sinai directly from Hashem, just like the rest of Torah shebal peh".

Similarly from the Alshich: "Nobody has a right in our generation to disagree based on his own opinion, if he did not find such an opinion from his predecessors (Rebbeim). We are commanded "lo sosur", which includes also Agadita." (Shmuel II 21:1)

The Sifri (48) explains the posuk in Devarim 11:22, "And you really follow all this Mitzvah", that "this means to learn Midrash, Halachah, and Agada."

Rav Yiztchok Izak Chaver in Magen Vtzenah (p, 49) - there are people who reject Chazal's statements because the secular scientists disagree (he gives examples, such as the sun rising above the firmament at night etc), and they laugh saying that we know it's not true. they are fools. The GRA, who even the scientists admit that he knew science much better than them, accepted all words of Chazal as fact, and that the philosophers and scientists (chachmei hatechunah) are all wrong, and he believed in the truth of the simple straightforward understanding of the words of Chazal. The GRA said that the scientists didn't come to the ankles of our sages in any secular discipline or science.

Chida (Shem Hagedolim: "Seforim":5:82) - There are a minority of Gedolim among us who disagree with Chazal because of their scientific knowledge, but they do not understand that Chazal had Eliyhau Hanavi informing them, and they had Ruach HaKodesh to inform them.