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In recent centuries, authorities such as the Chazon Ish, Rabbi Chaim Na'eh, and Rabbi Moshe Feinstein ruled on the exact size of a tefach, ammah, kezayit, and other shiurim. What did people do before these rulings? Did they just estimate the size of their own hands, or was there an unwritten tradition of some sort?

  • Presumably they used analogous measurements. How else would a kezayit be measured relative to an egg among Ashkenazim? – Noach MiFrankfurt Dec 1 '14 at 14:39
  • @NoachmiFrankfurt I don't understand your point. An egg is an egg and an olive is an olive. What does one have to do with the other/ – Double AA Dec 1 '14 at 20:25
  • @DoubleAA, a k'beitzah is often used as a synonym for kezayit among Ashkenazi poskim who were unaware of the dimensions of olives, as they have similar shapes. – Noach MiFrankfurt Dec 1 '14 at 20:34
  • @NoachmiFrankfurt I don't think the shape is relevant. One opinion in Tosfot does deduce a least upper bound for olives of 0.5 eggs but that's related to a proof from a Gemara, not shape of the object. – Double AA Dec 1 '14 at 20:36
  • @NoachmiFrankfurt: Can you provide an example for the fascinating claim that "a k'beitzah is often used as a synonym for kezayit among Ashkenazi poskim". I'm really curious about this. – Danny Schoemann Dec 2 '14 at 7:41
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The Mishna in Keilim discusses this. Essentially they guessed it, based on the average measurement.

Starting from Ch. 14:5, here are some of the measurements:

פרק יז - משנה ה: הָרִמּוֹן שֶׁאָמְרוּ, לֹא קָטָן וְלֹא גָדוֹל אֶלָּא בֵינוֹנִי ‏

The pomegranate [mentioned in previous Mishnayot] refers to a medium sized one. [Presumably a fully-ripe one.]

פרק יז - משנה ו: כַּבֵּיצָה שֶׁאָמְרוּ, לֹא גְדוֹלָה וְלֹא קְטַנָּה אֶלָּא בֵינוֹנִית. רַבִּי יְהוּדָה אוֹמֵר, מֵבִיא גְדוֹלָה שֶׁבַּגְּדוֹלוֹת וּקְטַנָּה שֶׁבַּקְּטַנּוֹת, וְנוֹתֵן לְתוֹךְ הַמַּיִם, וְחוֹלֵק אֶת הַמָּיִם. אָמַר רַבִּי יוֹסֵי, וְכִי מִי מוֹדִיעֵנִי אֵיזוֹהִי גְדוֹלָה וְאֵיזוֹהִי קְטַנָּה, אֶלָּא הַכֹּל לְפִי דַעְתּוֹ שֶׁל רוֹאֶה: ‏

An Egg-size refers to a medium size. Rabbi Yehuda says one brings the biggest one can find and the smallest one can find, puts them in a vessel full of water, and then one divides the spilled water. Rabbi Yossi says one uses one's best estimate of what seems to be an average size egg.

פרק יז - משנה ז: כַּגְּרוֹגֶרֶת שֶׁאָמְרוּ, לֹא גְדוֹלָה וְלֹא קְטַנָּה אֶלָּא בֵינוֹנִית. רַבִּי יְהוּדָה אוֹמֵר, הַגְּדוֹלָה שֶׁבְּאֶרֶץ יִשְׂרָאֵל הִיא הַבֵּינוֹנִית שֶׁבַּמְּדִינוֹת: ‏

A fig - refers to a medium sized one. Rabbi Yehuda says that the big ones in Israel are like the medium ones elsewhere.

פרק יז - משנה ח: כַּזַּיִת שֶׁאָמְרוּ, לֹא גָדוֹל וְלֹא קָטָן אֶלָּא בֵינוֹנִי, זֶה אֵגוֹרִי. כַּשְּׂעֹרָה שֶׁאָמְרוּ, לֹא גְדוֹלָה וְלֹא קְטַנָּה אֶלָּא בֵינוֹנִית, זוֹ מִדְבָּרִית. כָּעֲדָשָׁה שֶׁאָמְרוּ, לֹא גְדוֹלָה וְלֹא קְטַנָּה אֶלָּא בֵינוֹנִית, זוֹ מִצְרִית. כָּל הַמִּטַּלְטְלִין מְבִיאִין אֶת הַטֻּמְאָה בָּעֳבִי הַמַּרְדֵּעַ, לֹא גָדוֹל וְלֹא קָטָן אֶלָּא בֵינוֹנִי. אֵיזֶה הוּא בֵינוֹנִי, כֹּל שֶׁהֶקֵּפוֹ טָפַח:

  • Olives: Medium - i.e. Egori ones.
  • Wheat kernel: Medium - i.e. Midbari ones
  • Lentil: Medium - i.e. Egyptian ones
  • Thickness of cattle prod: Medium - i.e. circumference 1 Tefach

פרק יז - משנה ט: הָאַמָּה שֶׁאָמְרוּ, בָּאַמָּה הַבֵּינוֹנִית. ‏

Ama - arm's length - medium.

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    This is of course why they chose common objects as units of measurement. Little did Chazal think that Jews would end up living in a place like northern Europe with no olive trees – Double AA Dec 1 '14 at 14:45
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    @Double not they chose. The Torah chose. The chazon ish brings a medrash that says this. And anyways shiurim are one of the things misinai. – user6591 Dec 1 '14 at 14:54
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    @user6591 Actually I believe the Chazon Ish thought that any the Beis Din of any generation can decide what is the definition of each volume unit. IAE the Torah was meant to be kept in Israel so my point about olives stands – Double AA Dec 1 '14 at 20:23
  • Worth noting also that the Mishna in this answer postdates the Churban and still recommends using regular eggs, so we see the "shrinking of the eggs" didn't occur as a consequence of the Churban. – Double AA Dec 1 '14 at 20:24
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I heard the following from Rabbi Heinemann, in answering this question (specifically he was asked about R' Moshe's teshuva about the exact height necessary for a mechitza, which has a dearth of prior literature on the subject):

There is a famous story in which the Chofetz Chaim was upset because his children wanted to put a floor in his house (which had a dirt floor). He said "next thing you know you're going to want a clock!" What did the Chofetz Chaim have against getting a clock? If you don't have a clock, you err on the side of caution - you don't wait until the last minute to daven or to bentch licht, you make sure you do it well before you get into a period of uncertainty. In generations where they didn't have the ability to measure with more precision, they were much more careful - they knew an approximate amount, and they made sure they were safely within that range.

R' Heinemann suggested that it is really a testament to the lowliness of our generation that we have everything calculated out to the nth decimal point - because we are figuring out the least we have to do to get by. Once upon a time, they made sure that they got it right by going beyond the exact minimum/maximum.

  • It was probably a great deal easier to go beyond the exact stated minimum for certain volume shiurim when they were estimated based on the size of the things they described rather than calculated based on the size of other, unrelated things. – Isaac Moses Dec 1 '14 at 20:21
  • @IsaacMoses Why would it be easier? Do you mean more convenient? I assume that there was a margin of error, and you could make sure you go beyond it, no matter how much the margin of error increases. It may have been more expensive/inconvenient, but that is kind of R' Heinemann's point. – Y     e     z Dec 1 '14 at 20:27
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    I think he means it's easy to be machmir on a kezayis by eating 1.5x when it isn't already the size of ~14 olives. – Double AA Dec 1 '14 at 20:34
  • @DoubleAA so again, I don't know why that is called "easy." Might be cheaper. But does anyone have a problem with the math? – Y     e     z Dec 1 '14 at 20:37
  • @YeZ Expense matters, as does the ability to digest, as does accommodating the requirement of eating the korban (or afikomen nowadays) on a not-full stomach . – Isaac Moses Dec 1 '14 at 20:39

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