An 8th grade, 13-year-old boy asked me today why I accept what Rashi says in his commentary on Chumash. The 8th grader claims Rashi could be wrong you know. There were other commentators. He was not there, how does he know what really happened and why it happened. Here is the question: Why do we adhere to Rashi so much? Why do we accept our commentaries over any other type of biblical commentary?
I once heard a clever idea: Since Rashi didn’t have Rashi’s commentary, whose commentary did he learn? The answer is Rashi learned “roshi” – which means “one’s own head”.
Use this idea to encourage your student to apply his own thinking to understanding whatever he’s learning before consulting any commentary. Train him to ask questions, apply critical thinking, explore many possible approaches and explanations while simultaneously searching for proofs or refutations for all the possibilities he’s pondered. In short, convey to him the importance of learning “roshi” before looking into Rashi.
That being said, an essential part of Rashi’s “roshi” was the tremendous amount of information he acquired by applying himself day and night from early youth to learning the entire Torah – Chumash, Talmud, Midrash, Halacha – by heart. In short, Rashi knew the entire Torah such that it is not for naught that Rashi is said to be an acronym for “Rabban shel Yisrael” – the rabbi of all Israel.
Therefore, after learning “roshi”, one must lower one’s head in deference and awe for the scholarship of Rashi’s commentary which is culled and distilled from sources which most people don’t even know exist, and will probably never even see, let alone understand. Rashi’s commentary is so authoritative, then, not because he lived in those times or witnessed the events described, but because he delved with such depth and breadth into the sources of those who either lived then, or at least received a tradition or explanation from those who did.
Therefore, when “roshi” argues with Rashi, the response should not be why I’m right and Rashi’s wrong, but rather: “Why didn’t Rashi explain as I did”, or “Why didn’t I see it as Rashi did?”
Similarly, when others of the great commentators argue on Rashi, we are not qualified to mediate between such giants to consider one right and the other wrong. Rather we must marvel at the scholarship and genius of both commentaries, accepting both as diverging facets of the same truth. This is the spirit of the teaching of our Sages: “These, and also these, are the words of the Living G-d”. Of course, since the other commentaries saw Rashi, when they don’t argue with him (which is usually the case), they agree with him, and he is certainly right.
So the bottom line is, after applying “roshi”, we accept Rashi because he knew virtually the entire Torah while we know nearly no Torah – which is also the reason why we accept his opinion in particular, or the opinion of other of “our” Torah giants in general, over the opinion of what you refer to as “any other type of Biblical commentary” by which I understand from the context to mean not “ours”. Namely, the former knew the entire Torah while the latter, as intelligent and educated as they may be, know little of the “words of the living G-d”.