Thursday, March 30, 2017

The Kezayis Post

With Pesach approaching, it's kezayis season again. The monograph that I wrote on the evolution of the kezayis, from the size of an olive to a matzah ten times that size, seems to be the most popular piece that I have ever published. If you haven't read it, you can download it at this link. This year, I was sent a fascinating new piece of evidence that Chazal's kezayis was much smaller than the sizes popularly stated today. It's from the following Mishnah:
 טלית טהורה שהכניס ממנה שלש על שלש לבית טמא נטמאה. וטמאה שהכניס ממנה אפילו כזית לבית טהור טמאתו: 
A pure cloak of which a three-by-three [finger-length] piece entered an impure house becomes impure. [If it was] an impure [cloak], if he extended even the volume of an olive [of it] into a pure house, it makes [the house] impure. (Mishnah, Nega'im 13:8)
This Mishnah states that a piece of a cloak (which is a material approximately the thickness of matzah, or less), which is the volume of an olive, is less than three-by-three finger lengths. Unless you're going to say that people back then were much bigger (which indeed, some people do say), then we see that a kezayis of matzah is significantly smaller than about a quarter of a letter/A4-size piece of paper.

Here is a list of other posts relating to this topic:

Matzah/Maror Chart for Rationalists - so that you, too, can have a chart!

The Popularity of Olives - exploring why this paper is so popular and yet hated by some.

Why On Earth Would One Eat A Kezayis?  - discussing the strange notion that one should aim to eat a kezayis of matzah on Seder night.

The Riddle of the Giant Kezayis Defense - wondering why many people would not accept that a kezayis is the size of an olive.

Maniacal Dishonesty About Olives - exposing an error-ridden critique that appeared in the charedi polemical journal Dialogue.

It's Krazy Kezayis Time! - discussing the view that one should eat a huge amount of matzah in a very short time in order to fulfill all opinions.

The Kezayis Revolution - announcing the fabulous sefer by Rabbi Hadar Margolin, which presents the same arguments that I brought but in a more yeshivish manner. He also brings an astonishing array of evidence that many recent charedi gedolim likewise held that a kezayis is very small, including even the Chazon Ish! Best of all, the entire sefer can be freely downloaded.

Finally, two notes regarding The Biblical Museum of Natural History:

First, there are lots of tours over the next few weeks, including before Pesach as well as Chol HaMoed. But they are rapidly filling up, so if you'd like to come, book your tour as early as you can!

Second, we are really looking for people who support our goals of educating the entire spectrum of society about the relationship between Torah and the natural world, and who want to be part of our mission. To join the museum as a patron, please see for details. We can now arrange tax-deductible donations in Israel, the UK and Canada, as well as the US. For easy online donations, please click this link. Thank you for supporting our mission!


  1. I always thought the Rationalist spelling was....KezayiT

    1. Actually both Ashkenazic and Sephardic pronunciations of Hebrew are highly inaccurate: the correct, historical voicing of the letter ת without a דגש is th like the English word thaw.

      So really כזית = k'zai-yith

    2. For what it's worth, it's kezayiTH. Modern Hebrew is almost as bad as Ashkenazi Hebrew, in some ways worse.

    3. josh, I wouldn't be so sure of ancient pronunciations of Hebrew. We know that there were tribal differences as reflected in the 'shibolet(s)' test for the b'nei Efra'im (they, apparently, had difficulty with the combination 'sh' and 'saf' sounds. Your pronunciation of a 'taf' without a digest appears to be of Spanish origin which was carried over into English (for example, 'sabbath') by the original Spanish Sefardi immigrants to the new world.

      Y. Aharon

    4. While the 'th' sound may not be entirely precise, we know that both the Ashkenazi and Modern Hebrew pronunciations are wrong. Ashkenazim pronounce it such that it's indistinguishable from Samech or Sin, while Modern Hebrew doesn't differentiate between the two states at all.

      Growing up Ashkenazi, I have a preference for the soft pronunciation, because at least I am pronouncing it differently than a Tav.

    5. The Teimanim pronounce a weak ת as 'thaw' even among the different groups of Yemeni communities and tribes, they all agree on that particular point

      See Rabbi Bar Hayyims shiurim on this topic

      His youtube channel: machonshilo

    6. Hebrew pronunciation is impossible to reconstruct totally, see :

      Ancient Hebrew Phonology

      Modern Hebrew phonology

      Biblical Hebrew

      Pronunciations of Hebrew

      However is seems clear the letters BGD KFT have a plosive sound if they have a dagesh and a fricative (spirant) (soft) sound without a dagesh.

      In particular the D and T sounded like, and are still pronounced by most Yemenites as,

      D=d as in dot; d=th as in that; a voiced fricative

      T=t as in tow; t=th as in think; an unvoiced fricative.

      Note: the soft d allows the Echod of the Shmah to be emphasized as well as words like vavadtem and vleemadtem be pronounced as vsamtem without the difficulty of two plosive sounds together.

    7. Nothing's "right" or "wrong" strictly speaking. Hebrew was pronounced differently at different times and places.

      The problem of Ephraim was probably that "sin" had a pronunciation akin to the Welsh "ll", which is sort of a phlegmy "sh". Hard for non-speakers to distinguish from a "sh", or to make in this case.

      The beged kefet were probably originally (again, not strictly speaking an accurate term) b/v, hard g/ghayn (a letter in Arabic linked to 'ayin), d/eth (an Anglo-Saxon letter), k/kh, p/f, t/thorn (also Anglo-Saxon). Shin/sin gives us 29 consonants when you consider that every other letter (including vav, kuf, tet, etc.) once had their own sounds. Ashkenazi has only 20. Modern Israeli has...only 20, with one change, although some newscasters and the like try to distinguish their hets and ayins. That's not such a big difference.

      Vowels are a whole other story, similarly muddled, though.

  2. Not so sure about this proof.

    In the reisha, the idea is the minimum definition of a beged, so even if that was introduced into the house, it is something capable of receiving impurity (in its entirety?).

    Meanwhile, in order to convey the impurity, the amount needing extension into the house is that of a kezayit.

    That doesn't say that a kezayit is the entirety of, or a fraction of, a three by three beged. Rather, each is a specific minimum of a larger cloak.


    1. Respectfully disagree with R. Waxman. The mishna intends to contrast two different sizes to two situations: If 3x3 of a clean shirt enters a tamei room the shirt becomes tamei, but if the shirt itself is tamei, then *even as little* as a kezayis will be mitameh the room.

      The proof is good, I think.

  3. Isn't 3 X 3 fingers lengthwise quite large? Is this widthwise?

  4. Machon Shilo's Rabbi David Bar-Hayim agrees regarding the size of a k'zayit:

  5. In many ways its very upsetting to read this analysis. I am interested in one thing, Truth. The present day distortion of the "truth" is quite troubling. As the author points out people take such a simple and quite trivial matter and have taken it to a level that is rather disturbing. what else are we distorting? O yea, that's why we have Rav Slifkin! Keep up the good work!

  6. It should be pointed out that the small Kezayit holds everywhere. For example, for Birkat Hamazon the whole year. And for eating less than a Kezayit of Karpas during the Seder...

    1. That is a paradigmatic example of how the 'halakhic process" turned into halakhic paralysis. "Hilchot brachot is too hard so just sit there hungry till 10.30, problem solved".

  7. Giants

  8. Rav Slifkin, you'll be happy to know that this morning I saw Rav Margolin's sefer for sale in Kiryat Sefer.

    1. I'm even more interested to know that there are people in Kiryat Sefer who read this blog!

  9. Forgive please (and resolve) the ignorance, but what on earth is that visitor to the Museum holding over her shoulder?

  10. A pure cloak of which a three-by-three [finger-length] piece entered an impure house becomes impure. [If it was] an impure [cloak], if he extended even the volume of an olive [of it] into a pure house, it makes [the house] impure. (Mishnah, Nega'im 13:8)

    What do you take to be a finger length?


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