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39

Ralbag (Gersonidies) has the earliest known use of a proof by mathematical induction in his mathematical work Maase Hoshev (1321 CE). Source: Rabinovich, N. L. (1970). Rabbi Levi Ben Gershon and the Origins of Mathematical Induction. Archive for History of Exact Sciences, 6(3), 237-248. Available in JSTOR here. (For comparison, the prevalent thought ...


26

I would say the biggest explanation ahead of its time was not by the rabbis, but by the Torah, steadfastly defended by even the most rational rabbis in the face of prevailing secular thought. Up until 1929 (and perhaps even as late as 1949), the leading view in astronomy was that we lived in a steady-state universe with no beginning and no end. People often ...


22

First look up the sources people quote, so that you know what they're saying inside. Then, when you ask you Rav, tell him I had this question and did some research. This is what I found, what is the practical Halacha? You can tell him where you got the idea about which sources to look up, but at that point it shouldn't matter. You're not telling him that ...


22

Because "Alfasi" is really "al-Fasi". "Al-Fasi" is Arabic for "the Fezite" (Fez being the city in Morocco where he lived). So kind of like how the word "of" gets swallowed in "USA", the word "the" got swallowed in "Rif". Wouldn't have made much sense to make his acronym stand for "Rabbi Yitzchak The".


21

Shalom u'Vracha, Thanks for your interest in Sefer Iyunei Deah/Procedure for semicah by R. Z.N. Goldberg, shlita. Below is a standard response I prepared based on many people's questions. Not everything below may pertain to you, but hopefully your questions will be among those addressed. Please feel free to contact me if you are interested in further ...


21

This practice seems to be (at least) as old as the Gemara, as the Gemara states in Brachos 27b: 'R. Yirmiah b. Abba is different, because he was a disciple-colleague. [This can be proven by the fact that] R. Jeremiah b. Abba said to Rav: Have you made havdalah? He replied: Yes, I have; and he did not say to him, has the master made havdalah' In ...


20

A Rabbi is an expert in his field and has studied for many years. If one needed medical advice, G-d forbid, they would never rely on "crowd-sourced" opinions of a question and answer website, but would go to a trained doctor with practical experience. If this is so with regards physical healing, how much more so when dealing with the health of one's souls. A ...


20

Yes, the painting is based on a popular picture of the Chofetz Chaim, which can be seen in The Schwadron Collection of the National Library of Israel (Jerusalem). The archive lists the picture as following: A photo portrait of Rabbi Israel Meir Cohen ("Chafetz Chaim"): printed silver, black and white, 7X12 cm. Portfolio also includes a copy of this ...


19

My understanding (no source) is that, yes, twentieth-century rabbis kept copies. It wasn't necessary to type twice: they used carbon paper. I don't know about older rabbis, though. Update: However, see the comments on this answer.


18

The issue we have to ask is why is a psak (legal ruling) ever binding in the first place? Why can't you just ask the next person? There are two main possibilities (see Shach YD 242:31): שויה אנפשיה חתיכה דאיסורא The asker accepted upon themselves when they asked the first authority to follow their answer. Let's assume for now this principle works similar ...


18

Semikhah is the name of the process through which a rabbi is ordained in Rabbinic Judaism.


17

Dr. Jeremy Brown, in a post on his Talmudology blog on science in the Daf Yomi, points out that Rava, quoted in Yevamot 97a, provides the first published claim that boys' puberty can be delayed by their being either overweight or underweight. כי אתו לקמיה דרבא אי כחוש אמר להו זילו אבריוהו ואי בריא אמר להו זילו אכחשוהו דהני סימנין זמנין דנתרי מחמת כחישותא ...


17

I think the Ba'al Shem Tov had to have existed in some way (even if it's not the way we've been taught), as I doubt an entire branch of Orthodox Judaism would base itself off the teachings of a ficticious figure. Let me ask you this - if the Besht didn't exist, who made him up? From a historical standpoint, saying he didn't exist is futile. We have books ...


16

See the sefer Pardes Yosef on parshat Teruma chapter 25 sub ubb"b d"y [= ubibava batra daf yod] where it is described how the Besh"t was asked about a Talmudic source which says that every Torah prohibition has a permitted aspect to it, so where is heresy permitted? His answer was that in performing the mitzvah of charity, one should help the poor man as if ...


16

Virtually unarguable? God Himself is called "Gadol" by King David in Psalm 145:3. To this day, I don't think anyone would disagree on that one. גדול יהוה ומהלל מאד ולגדלתו אין חקר The Lord is great and very much praised, and His greatness cannot be searched. (Chabad.org translation)


16

Be'er Hagolah at the end of Yoreh Deah 334 lists the following: Not to marry more than 1 wife. Someone who is in Cherem should not be a Shaliach Tzibur. A person should not be away from his wife more than 18 months. Not to rent a house from a non Jew if a Jew is living there. Not to cut off the margin of a page of a Sefer, even to write on it. Not to ...


16

As mentioned by @WAF, R' David Zvi Hoffman wrote a response to bible criticism in the early 1900's which is available on Daat.co.il. Umberto Cassuto, while not strictly orthodox, published a book in reply to the DH in 1941. There are some notes on it here, and a new edition is available online here: http://www.shalempress.co.il/download/Products/...


16

There are, perhaps, several factors to consider: In Chabad thought, the rebbe is more than just a leader, Torah teacher, spiritual guide, etc. All of these roles, and many more, are outgrowths and expressions of his being the נשמה כללית, the "all-encompassing soul" of the Jewish people (see Tanya, ch. 2). Now, of course, barring an explicit statement by ...


15

R. Yehuda Aiash (Shut Beit Yehuda YD 28) rules that in general any honour which one must accord a male (such as standing up for an older man), one must accord an equivalent female as well: פשוט דכל מיני כבוד שחייבין לעשות לאיש הה"נ לאשה Similarly, R. Yitshak Attiya writes (Zera Yitshak: Pilpelet Kol Shehu p. 88, cited in Yalkut Yosef 627 p. 173) cites ...


14

In the days before copy machines and email it was certainly a common process among many letter writers Jewish and non-Jewish alike to write out copies of their own letters that they were sending. Not everybody did it but it was quite common. You can therefore find collections of letters sent by many people famous and not famous in historical collections. The ...


14

I think that by the Lubavitcher Rebbe the secretaries used to make a rough draft, send it in to the Rebbe for proofreading, get the Rebbe to write notes on it, retype the letter and send it. Therefore, the secretaries had the original copy in manuscript. Later, when the Rebbe stopped writing full letters, He used to respond in Ksav Yad on the margins of the ...


14

I have an old copy of The Jewish Observer that discusses the ban. It seems a couple comments in his translation of the Talmud implied that certain sages ruled consistently in a particular fashion (e.g. stringently) because their personality inclined in that direction. Some were worried that readers would infer that the sages were allowing their personal ...


14

Rabbi Y.L. Rapaport suggested that R' Yehoshua Ben Chananiah's statement (כוכב אחד לשבעים שנה עולה ומתעה את (הספינות (בבלי מסכת הוריות דף י עמוד א) This is thought to refer to the periodicity of Halley's comet, about 1500 years before Halley discovered this. In regards to comments suggesting that this claim is unfounded, I note that several reputable ...


14

The question as currently phrased is asked by, among others, R. Yosef Albo in Sefer HaIkarim 3:23 (which is why I'm unsure as to why it still has a negative score). Since I don't have a better way of doing this, I'm going to just paste here what I wrote to this similar question, with a couple of variations. 1. Idiomatic Expressions Some differences between ...


13

Its only considered a psak if it's a new case that requires original analysis. If you are just reciting a halachik fact, it is not a psak halacha. It does not require a posek and the person can still go and ask someone else. (I heard a similar statement b'shem R' Hershel Schachter).


13

Chavos Yair (152) discusses a number of these cases. In some of them, he says, the person delivering the insulting remark is the other one's teacher; the halachah is indeed that if a teacher sees that his students aren't applying themselves properly to their studies, he should "get angry at them and insult them verbally" to spur them to correct behavior (...


13

The story is a well-known piece of Jewish folklore, and it is hard to know if the story is true at all, and if it is, how much it may have changed over the generations. The story can be found in the sefer Michtavei Chofetz Chaim (p.262) at the beginning of an essay written in honor the shloshim of the Chofetz Chaim. It was originally published in the ...


13

If someone is born to a Jewish mother, regardless of her affiliation or observance, that person is 100% Jewish and allowed to marry another Jew. There is no conversion involved. I guess that this rabbi, in this situation, wants documentation that demonstrates that your friend's mother, and therefore your friend, is indeed Jewish. There are various ways this ...


13

Shemaya and Avtalyon, two great rabbis from the 1st century BCE, are identified in the Talmud (Gittin 57b) as converts. So it seems that converts can become rabbis, and even important ones. I know of no sources that imply the law on this matter was different before that point. See also this question: Can a convert be a prophet?


13

The Tzla'ch in Berachot 26b says the גמרא can't ask on Rebbe Yehoshua ben Levi from a ברייתא because he lived at the end of the Tannayic era and, therefore can argue on a ברייתא


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