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41

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 before ...


29

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

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 ...


21

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 ...


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 ...


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

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 ...


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

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 ...


17

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 ...


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

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 ...


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

Click here to see this video that has been making the rounds on Jewish sites recently has a short scene of the Chafetz Chaim. Here are some screen caps:


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 ...


14

The term "rabbi" means that the person received semikha (not to be confused with the modern form of semikha which is different). There was no semikha in Bavel, so none of the amoraim who lived there were "rabbi" unless they came to Eretz Yisrael. An easy way to remember this is by looking at the last letter of the word. "Rav" ends with ב which is also the ...


13

If we're counting mathematical comments by rishonim (Medieval Scholars), then in addition to @DoubleAA's reference to Ralbag (Gersonidies) who has the earliest known use of mathematical induction, other Jews have made some strides here as well. R. Avraham bar Chiyya has an interesting proof that the area of a circle is equal to half its radius times ...


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


13

The ש"ך wrote a commentary on the שולחן ערוך. The ט"ז argued with many of his rulings. The ש"ך responded in the נקודת הכסף. The ט"ז responded again in the "דף אחרון". And the ש"ך responded to that in "קונטרס אחרון". (source) In the הקדמה to the נקודת הכסף in יורה דעה, the author, the ש"ך, writes (see there): אל יעלה על לב הקורא בספרי זה שמפני שהיה לי ח"ו ...


13

Yes, but it's not recommended- The "orchestrator" of the wedding makes sure nothing goes wrong. The sages say that anyone who does not know the marriage laws well should not get involved with them (kiddushin 6a), as many mistakes can result. פרש"י : בטיב גיטין. בהלכותיהן : לא יהא לו עסק עמהם. להיות דיין בדבר שמא יתיר איסור ערוה וזהו עיוות ...


13

If you find that your questions are not being received as they were intended and they were asked with the proper deference (כבוד רבך ככבוד שמים), perhaps you need to ask your question of authorities who are willing to address it, or are comfortable saying they don't know the answer - but may research it. Or, you can ask your question here where you have a ...


13

Among those Rabbis that I know, if/when they are approached by someone who wasn't raised as a Jew but has a Jewish maternal grandparent, they welcome them with open arms as Jews, albeit Jews who have been estranged from their own religion. I have known this to have occurred on multiple occasions (although I was never personally involved in any). It may be ...


13

Beer Heitev to Orach Chayim 89:3 (ד״ה מותר) quotes the Pri Chadash saying: Coffee can be drunk (before prayer), particularly in Egypt where their thinking doesn't work properly without coffee. וכ"כ הפר"ח דקאו"י יכול לשתות ובפרט במצרים שאין הדעת מתיישב בלא קאו"י אבל קאו"י עם צו"קר או כל מיני תרגומא כדי שלא לשתות הקאו"י ...


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