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Rashi almost certainly never saw an olive. The same goes for other medieval authorities in Ashk’naz (Germany-Northern France). This little-known but indisputable fact should matter to you. It has everything to do with the following question: Is Halakhic Judaism rational and rooted in reality, or is it a hypothetical construct unconducive to engaging the real world?

It is a simple matter to ascertain, or describe to another, the volume of an average olive, a ‘k’zayit’…provided you have olives. But what if you have never seen an olive? How would you understand the concept? How would you describe it to someone unfamiliar with olives?


This was the reality in Ashk’naz in the Middle Ages, and there is no mystery as to why. The olive tree is native to the Mediterranean basin, from Israel in the East to Spain in the west; it does not naturally grow elsewhere. In Roman times, due to the trade routes which crisscrossed the Empire, olives may have made their way to Germany and beyond. The collapse of Rome, however, led to a breakdown of law and order, and therefore trade.

Medieval Ashk’nazim were unfamiliar with olives, a fact confirmed by R. Eliezer b. Yoel’s (d. circa 1225) discussion of the minimal amount required for a b’rakha aharona: “Wherever a k’zayith is required, one needs a sizeable amount of food, because we are unfamiliar with the size of an olive…” (Ra’avya, B’rakhoth 107).

Some Ashk’nazi authorities concluded that an olive was half the volume of an egg, while others demonstrated, based on Talmudic sources, that it must be less than one third of an egg. How much less they could not say. The truth, of course, is different, as was clearly perceived by one 14th century authority who actually made it to Eretz Yisrael. Responding to the proposition that a person could swallow three k’zaytim at once (which is quite impossible if one assumes a k’zayit to be half of an egg in volume) he wrote: “As for me, the matter is plain, for I saw olives in Eretz Yisrael and Yerushalayim, and even six were not equal to an egg.” S’pharadi authorities, on the other hand, had no such difficulties. One wrote that an olive is “much less” than a quarter of an egg (Rashba), while another mentions in passing that a dried fig is equal to “several olives” (Rittba). The last three statements, made by sages who saw olives, are entirely accurate.

In present day Halakhic practice, predicated on opinions rooted in the aforementioned lack of knowledge and experience, a k’zayit is often said to be 30 cc, while others say 60 cc. These figures bear no relation to the real world olives of Eretz Yisrael which average 3-5 cc. It is claimed by some that once upon a time olives were much larger. This claim is false. Olives and olive trees have not changed, as evidenced by the fact that there are over 70 olive trees in Israel ranging between 1,700-2000 years old, and 7 are approximately 3000 years old. These trees continue to produce fruit identical to the olives of younger trees. Halakhic responsa from the G’onic period echo these facts, stating plainly that olives do not change. Some would have you believe that there are two kinds of olives: real olives and ‘Halakhic’ olives. In their view, Halakha need not reflect reality; it exists in an alternate reality of its own. This is a tragedy because it paints Judaism as divorced from reality and irrelevant to a rational person. This is a lie because Torah was intended by Hashem as our handbook for operating in the real world.

The ultimate purpose of Judaism was announced by the Creator before He transmitted the Torah to His people: “And you shall be for My purpose a kingdom of priests and a holy nation” (Exodus 19:6). The nation of Israel is the priest connecting God and mankind. “I, God, have summoned you for a righteous purpose…. and have assigned you for my covenant with humanity, a light for the nations” (Isaiah 42:6).

The Jewish people, in order to succeed, have to live and lead in the real world. To deal with the challenges facing us as a nation we must think, act and believe rationally. A rational person does not believe in olives 2o times the size of the olives we see with our own eyes. To deal with reality, we have to get real.

We are described as being created in the image of Hashem because we can think and reason. To convince ourselves that Halakha can be based on irrational claims is an insult to our God-given intelligence. Not to mention that it places Judaism squarely in the realm of fairy tales. What kind of message does that send to our children?

Nothing could be more pernicious than the notion that truth and Torah do not mix. The same goes for the idea that Halakhic opinions rooted in Exile-induced misconceptions are sacrosanct and immutable. A philosophy that turns aberration into truth, the Torah of Galuth into the real McCoy, is intolerable. The clear implication is that Judaism, as a system, is broken and beyond repair.


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Rabbi David Bar-Hayim is the head of Machon Shilo, a centre of Jewish learning in Jerusalem dedicated to the exposition and dissemination of Torat Eretz Yisrael. The teachings of Rabbi Bar-Hayim may be found at


  1. I liked this rabbi’s auccinct and well constructed arguments. It could certainly make the Seder/s so very much mre pleasant not to stuff oneself out f a misconception of what makes a kayzaith and concurrently makes our stomachs distended not t say what it des to the rest of us for days to come.

  2. To ZK: The volume of an olive is a straightforward, readily apprehended amount which any person can judge in an instant. See the Mishnah in Kelim 17:6. I’m guessing that you feel the amount should be updated to, say, 5cc. Most people cannot look at a piece of food and judge whether it is 5cc or not. They would have to measure. Chazal did not think that the Torah was given only to those who can measure. It is for all Jews, and it is supposed to be simple and seamless. A kezayis is as simple as it gets.

  3. There is absolutely nothing fascinating about the unfortunate continuation of R' Bar Chayyim's Napoleon complex, with another article which purpose is to state "Bar Chayyim is teh smartest and most knowledgeable man in the Universe, while all Rishonim are retarded idiots who don't even know how an average olive looks". Truth is, all rishonim had an idea how olives look like, they just didn't know what "Zayit Agori" mentioned in Mishnah Kelim, whether it's a specified species or the average olive, and thus chose to deduce the shiur from the size of beit blia, which is approximately two kazayit and one kabeitza (E"E Kritut 14a – Yoma 80a). There are absolutely HUGE olive species. Perhaps BH knows less about the fruits of Eretz Yisrael than Baalei Hatosefoth in France.

  4. I happen to have been reading the work of both Rabbim for years. This is not a rip off of either by either. Ever heard the saying, "Great minds think alike" Please be more careful in your comments about other people.

  5. How would you describe the volume of an object in such a way that it would be understood for the next 2,000 years? Simple – take a common object that almost everyone is familiar with. Why wouldn't it be the relevant standard today?

  6. David I. Waxman While you and Avi may be right that measuring by k'zayis is still as relevant as it was +/-2000 years ago, I cannot accept your argument. The whole point of the article is that for many Jews for many years the olive was not a common object that everyone was familiar with, and that is why mistakes were made in shiurim. I'm not sure there is any way to ensure that you will be understood 2000 years from now, we are all human after all…

  7. Rabbi Slifkin wrote a blog about Rav Bar-Hayim’s article and did not mention your concern. Evidently he disagrees with your “feelings”. You should study up about kevod talmide hachamim.

  8. 1) Rav Bar-Hayim produced two explicit quotes from Ashkenazi Rishonim. In one quote, the Raavya states that he is unfamiliar with olives. But you, somehow, know better. You claim that Raavya and ALL Rishonim knew what an olive is. How do you know what ALL Rishonim did or did not know?
    2) You claim that the Rishonim were not sure what was meant by an average or egori olive, but most certainly knew what an olive looked like. Do you have a source to support your claim? I doubt it, because not one of the Rishonim writes this. Your claims are based on a childish and naïve view of reality.
    3) In the other quote brought by Rav Bar-Hayim, another Rishon states that he knew how many olives are equal in volume to an egg because he had seen olives in Eretz Yisroel. Why did he have to wait to get to Eretz Yisroel to know this?
    4) Rav Bar-Hayim does not suggest that “all Rishonim are retarded idiots”. He claims and proves that Rishonim in certain countries had no direct experience of olives, whereas Rishonim from other areas did.
    5) Rav Dov Lior of Kiryas Arba makes the same claim as Rav Bar-Hayim regarding Ashkenazi Rishonim: see @ 17 mins. Does Rav Lior also suffer from a Napoleon complex?
    6) It is apparent that you have a personal issue with Rav Bar-Hayim and lack derech eretz. Shame on you.

  9. HaRav David Bar-Hayim has held the halakhic position of the k’zayit being precisely that, an olive size for many years, way before the essay by Rav Slifkin so it is ridiculous to make a claim that his thinking is not “original.”

  10. Halakhah is not "as real as it gets". There is a difference in kind between trying to describe reality, and between defining law. We have other cases where law was based on things we currently do not believe about reality. E.g. The notion that maggots found within meat are kosher because they are produced abiogenetically from the meat. Or that one may kill lice on Shabbos, because they too are not born through sexual reproduction. Or that one may violate Shabbos to save a baby born prematurely in the 7th month, but one born in the 8th month isn't going to survive anyway the gemara tells you not to violate Shabbos to save it.

    And there are numerous approaches to how to deal with those issues. Some reexplain the law using today's understanding. Perhaps because the difference between our sages' notion of reality and what's really there isn't halachically significant. Others, such as the Vilna Gaon and Rav Kook, allow the new scientific knowledge to cause new stringency, but not new leniency. But none allow dismissing established and accepted law. Simply because generations of widespread acceptance creates legal authority.

    Technical knowledge about the size of olives in the classical period similarly would have little impact on binding law. Undoing law requires proving it is illegal. Not simply that it is superfluous or without a meaningful cause. So, for someone for whom more than a minimum of matzah would be dangerous (ciliac or other gluten intolerance, diabetes), who would thereby be violating laws about preserving health, now have grounds for leniency rather than stretching their medical limits. Similarly when the error in olive size means overestimating how rapidly a sick person would eat on Yom Kippur, we may be forced to adjust the top limit. In those cases, the error leads to legal flaws.

    The Oral Law is just that oral. Drift was built into the system. We aren't preserving facts, we are working a legal process. The issue isn't empirical accuracy but legal authority.

  11. While there is variation in the size of olives, there is still greater variation in the size of eggs. Micha, in NJ compare the size of a Small to a Jumbo, then compare the size of a Large in NJ vs in Israel. Who is to say what the size of medieval German or French eggs were compare to Mesopotamian eggs?

    A Happy Kosher Paysach (when did the segol become a tzayray?) to you and your family.

  12. Abe Kohen We have remains of olives found at Masada. So, eggs or no eggs, we know that all accepted opinions about the kezayis are bigger than they were historically.

    I'm arguing that all of this is interesting theory, but only of marginal import WRT law. Law based on misunderstanding the facts is still law — authority comes from acceptance. As long as the mistake about realia doesn't lead to a legal problem. This whole focus on halakhah as fact-finding misses what halakhah is.

    English needs a type system for its nouns, so that law and empirical datum wouldn't be mistakenly interchanged.

  13. Micha Berger, Maimonides also says, does he not, that all we have left is to interpret the words of the Talmud? Perhaps I'm the bigger parliamentarian here than I thought…

    What difference is it to research the olive discussed in the Talumd than for a Rishon to use an alternate girsah or his own reasoning to determine his view of what the Talmud is saying?

  14. Ira Tick It's not an error to go beyond the requirements for the sake of conformity. Therefore, an overestimate isn't a *legal* issue when discussing the minimum to be eaten, only maxima.

    According to Maimonides' reason for that statement, that is no longer true once the Shulchan Arukh plus Mappah was accepted. He says the talmud is the last work where the acceptance spread across all of Israel. Well, with the exception of Bal'adi Teimanim, the same can be said of the Greater Shulchan Arukh — which is more widely accepted than the Babylonian Talmud was in M's day, actually.

  15. I meant error in terms of realia, not that one who eats more to conform is erring in practice, as in doing anything wrongful.

    I hear your point about the SA, and I can't say I don't wrestle with it. But I was thinking right after my last response that the acceptance of the SA is conditional in a way that perhaps the Bavli is not. The SA's authority is only to interpret the Talmud. Once the error–again, academically, not normatively–of the SA in interpreting the Talmud is made clear, I'm not sure the widespread acceptance of his words is meaningful.

    Food for thought, though. 😉

    I had a conversation with a young woman last year at this time about "deconstruction" and Rabbinics. I pointed out the ultimate folly of attempting to deconstruct it all back to Sinai, but I defended a middle ground that I think is firmly rooted in Jewish tradition–and Slifkin seems to believe this and marshals sources to support him–which is to accept the Talmud as the most authentic starting point for understanding the Law and implementing it, both in terms of substance and authority. I won't say there aren't problems with this approach, but I think it's reasonable in a way that preserving the rulings of later authorities, even the SA, is not, particularly in a case of clear substantive error.

  16. Don't want to beat a dead horse to death, but how do you extrapolate from a fossilized olive (or just olive pit) to size of a Middle Eastern olive 2000 years ago. Do you see variations in size between olives from different regions? I do.

  17. Abe Kohen I was just repeating other's results. Here are the details: You can check a 2,000 yr old olive tree and the olives it's still producing. The pits just tell us which breeds of olive were normally eaten; i.e. which ancient trees to check.

  18. Micha Berger Like the hockey stick problem in climate pseudo-science, we don't really have data on the climate conditions 2000 years ago. Perhaps they had a lot more rain. Perhaps the soil was more amenable to producing giant olives. In fact when we lived in California I had a garden where we grew all kinds of vegetables. But when I took 3 weeks to go to Israel I had to be creative with irrigation. So I took one gallon milk jugs, filled them with water, and stuck them in the fertile ground inverted. Came back and had some real giant vegetables. What I'm saying is: frankly we don't know. That, by the way, is something that took me a long time to admit. Lack of knowledge is not a bad thing. Hag Sa-me'-ach.

  19. Okay I have two words for you Zeke:) Yom and Cubit. 🙂 Standardized measurements are historically a real pain in the collective rears of those trynig to interpret them when they become obsolete do to a material change in a culture. (yes I used to be one of those pesky archaeologist) 🙂 At least an olive, even a super colossal, has a lower and upper range that has a good shot of staying consistent over time barring radical change in the evolution (or GM) of Olives :). As Micha above pointed out there are remains of olive pits in Masada, so question solved. As for Medieval trade, France at the time of Rashi most certainly DID have trade with Spain and the Middle East with the first crusade. The whole argument is a fallacy now as we know how big the olives were.

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