1.  Animal Sacrifices:
Maimonides presents the principles of the faith in his commentary on the Mishnah, “the Book of the Lamp" (In its original Arabic:"Kitab al-Siraj”; Hebrew translation “Sefer HaMaor” or “Peirush HaMishnayot.”).  In the introduction to the 10th chapter of Sanhedrin, Maimonides lists the 13 Principles of the Faith.  He asserts that “Anyone who doubts even one of these has exited the category of Israel”:
The Ninth Fundamental Principle is the authenticity of the Torah, i.e., that this Torah was precisely transcribed from God and no one else. To the Torah, oral and written, nothing must be added nor anything taken from it, as is said, “You must neither add nor detract” (Deut. 13:1).We have already sufficiently explained this principle in our introduction to this Commentary on the Mishnah. (trans. Maimonides Heritage Center, mhcny). 

Commentary on Mishnah
The Torah has been literally instructed by the Creator, by no one else.
The Torah is G-d’s permanent word, and no one else can change it. Nothing can be added to or subtracted from either the Written Torah or the Oral Torah. The Torah says, “Thus you shall not add to it, nor subtract from it.”

Popularizations of this principle appear in the daily prayerbook, as listed in “Best Jewish Studies” compiled by Prof. Rabbi Ahron Daum:

אֲנִי מַאֲמִין בֶּאֱמוּנָה שְׁלֵמָה, שֶׁזּאת הַתּורָה לא תְהֵא מֻחְלֶפֶת וְלא תְהֵא תורָה אַחֶרֶת מֵאֵת הַבּורֵא יִתְבָּרַךְ שְׁמו.
 
I believe with with perfect faith that this Torah will not be changed, and that there will never be another Torah given by G-d.

Yigdal
 לֹא יַחֲלִיף הָאֵל וְלֹא יָמִיר דָּתוֹ. לְעוֹלָמִים, לְזוּלָתוֹ:
 G-d will not replace nor change His Law for all time, for anything else.
 
Note: This principle has clear polemical value.  It obviates the claims of Christianity and Islam, specifically, that later revelation has superseded the Torah.  It inoculates the Jewish world against future enthusiasts.  It may fit Maimonides definition of a “necessary belief.”  

Does it also fit his definition of a “true belief”?
Maimonides argues for the principle on purely logical grounds: “’The Torah of the Lord is perfect’ 9 Psalms 19:8), and a perfect thing cannot be the subject of any additions or deletions.  Therefore it is impossible for it ever to change” (Guide 2:39).

Don Yitzhak Abarbanel (or Abravanel), in his Rosh Amanah (Principles of Faith), raises objections to the principle: 

It is still possible that there might be a change in it in terms of its recipient.  I mean to say that God might add to, or subtract from, or change the Torah at some time, either in its totality or in part, in accordance with what is best for its recipients.  Have we not seen that He gave Adam special commandments, and did not permit him to eat meat, while he gave Noah other commandments and permitted him (to eat) meat?  He gave the commandment of circumcision to Abraham and added many other commandments to Moses since divine laws change according to [the needs of the] time and in accordance with what is best for the recipients? (translation by Menachem Marc Kellner 67).

Abarbanel undermines Maimonides’ proof text by noting that “you shall not add to it nor detract from it” (Deut. 13:1) “only admonishes us to add or to detract from the commandments on our own authority.  But what is to stop God from adding to or detracting from the commandments?” (68).

Abarbanel cites Rav Hisdai Crescas who proposes that the Torah could be perfect, and yet could be changed to a different, but equally perfect, Torah (120).

Abarbanel marshals arguments which he considers definitive in supporting the Maimonidean principle that the Torah will never change.

Abarbanel notes several Midrashic texts that clearly predict change in the Torah in the future:

From Vayikra Rabbah: “All the holidays are destined to be abrogated except Purim and the Day of Atonement” based on Jeremiah 23:7-8.  
From the Midrash Tanhuma: “Why is the pig called hazir [apparently from the root h.z.r which means ‘to return’]? Because in the future God will return it [ha-haziro] to Israel.”
Another similar example appears in Vayikra Rabbah: “All the sacrifices are destined to be abrogated except the Thanksgiving offering” (27:12 and Midrash Soher Tov to Psalms 56).  This example seems directly to anticipate a world with fewer sacrifices than the Torah currently commands. 

Marc Shapiro devotes a chapter of his book, The Limits of Orthodox Theology: Maimonides’ Thirteen Principles Reappraised, to authorities who question or deny the principle of Maimonides that the Torah will never change.

Note the opinion: "There is no difference between this world and the days of the Messiah except [that in the latter there will be no] bondage of foreign powers" - b. Talmud, Berakhot, 34b and elsewhere.  In Shabbat 151b, the Talmud contrasts this opinion with that of R. Shimon ben Elazar: “‘until the days come when you will say “I have no desire in them”’ (Kohelet 12) refers to the days of the Messiah, when there is neither merit nor guilt.”

Consider the two alternatives. First, R. Shimon ben Elazar believes there will no longer be the opportunity to observe commandments or to transgress.  Will we then offer sacrifices, as the Torah commands, or will we then not have the opportunity, or need, to offer sacrifices?

Second, Samuel believes that we will still perform mitsvot in the days of the Messiah. The order of the world will not miraculously change. Will we have the Temple and sacrifices restored?

Maimonides clearly thinks so. In the Mishneh Torah, he rules according to Samuel; but in The Laws of Kings and their Wars 11:1, Maimonides explains that the Messiah will restore the Temple and reinstate sacrifices.  In the laws of Meilah (Misuse of Sacred Materials) 8:8, Maimonides quotes the ancient rabbis on the central importance of the sacrifices.   And this position seems entirely consistent with his own Ninth Principle, that the Torah has not, and will not, change. 

Our prayer book calls on us to reiterate the request that we will once again offer all the sacrifices in the future.  You can easily see this in the formulae of Korbanot in each morning service, and in the Musaf on every Rosh Hodesh or festival.

Maimonides himself, however, offers a seemingly contradictory account for the origin and function of sacrifices.  In the Guide of the Perplexed, he explains that sacrifices in the Torah exist as an elaborate stratagem on the part of the Creator to wean us away from idolatrous sacrifices (3:32, 46).  Maimonides articulates a gradualist conviction that nothing in nature tolerates swift transitions.  Babies must drink soft foods before they can chew plants and animals. So too, people in antiquity could not understand a religious practice without sacrifices.  The Torah restricts sacrifices in place, to the Temple, and restricts who may offer sacrifices to the Kohanim, and occasions on which we may offer sacrifices, to when we are ritually prepared (Tahor).  In the Guide, Maimonides clearly implies that we have outgrown sacrifice.   
Ramban strenuously objects to this account of the origin and use of sacrifice.  For Ramban (see his comments on Lev. 1:9), a human who brings a sacrifice vividly experiences what ought to happen to him or herself, and so comes to reevaluate his relationship with God.

Rabbi Ari Zivotovsky, in an article devoted to debunking the idea that major Torah thinkers anticipate a world without sacrifices, nonetheless admits some exceptions: 

Despite all that has been said, there are rabbinic authorities (none of whom were the stature of Rambam or Rav Kook) who suggest that animal sacrifices might not be reinstated in the days of the Third Temple. The Ashkenazic Rabbi Simcha Paltrovitch (d. 1926; Simchat Avot [New York, 1917], 7-8) says that while the Torah can never be changed, instead of actual sacrifices, those sections of the Torah dealing with korbanot will be interpreted via “remez” or “sod.” Alternatively, he suggests that in the seventh millennium there will be a Messianic period where animal sacrifice will be reinstated; however, in the eighth millennium there will be a more rarified period where animal sacrifice will not be practiced. As part of a long list of potential “changes” in halachah, the Moroccan Rabbi Yosef Messas (d. 1974; Otzar Hamichtavim, vol. 2, no. 1305, 249-251) suggests, based on Rambam, that it is possible to say that in the future there won’t be animal sacrifices, or that there will only be the Korban Todah (an animal sacrifice). Rabbi Chaim Hirschensohn, from Bayonne, New Jersey, and a brother-in-law of Rabbi Zvi Pesach Frank, also envisions a Third Temple without animal sacrifices (Malki Bakodesh, vol. 6 [Jerusalem, 1928], 96 and elsewhere). He has a novel explanation for the origin of sacrifices and it was to him that Rav Kook wrote the letter (cited in Iggrot HaReiyah) explicitly stating that there will be sacrifices. For more about Rabbi Hirschensohn’s position on sacrifices (Vayikra Rabbah 9:7), see Marc Shapiro, The Limits of Orthodox Theology (Oxford, 2011), 128-130 and online: http://seforim.blogspot.co.il/2010/04/marc-shapiro-r-kook-on-sacrifices-other.html.

However, I once had the privilege of asking a major talmid hakham whether he thought we would bring animal sacrifices in the 3rd Temple.  I will not use his name here (no, not R. Eliezer Cohen) because I did not ask his permission to share his opinion.  His reply: “Of course not.” 

I conclude this discussion with the stirring words of Yeshayahu HaNavi: “Even those I will bring to my holy mountain and make them joyful in my house of prayer. Their burnt offerings and their sacrifices will be acceptable on my altar; For My house will be called a house of prayer for all the peoples" (56:7).

2. Vegetarianism
At first glance, vegetarianism appears to present no issues in halakhah. Although the laws of kashrut permit meat, we have no obligation to eat everything kosher. 

Surprisingly, R. J. David Bleich published a concerted attack on vegetarianism in Tradition.  Rabbi Bleich objected to vegetarianism for several reasons, but primarily for adopting an autonomous higher standard in place of the heteronomous halakhah.

In the ensuing months, R. Bleich mitigated his stance by explaining that he had no objections to vegetarianism for health reasons, nor for stringent standards of kashrut.  He objected primarily to acting upon ethical or moral sensitivities apart from the Torah.

Another argument supporting meat eating appears in the Talmud, specifically in regard to the joy of the festivals: “there is no joy but with meat and wine.” However, the Talmud concludes that this statement applies to the meat and wine of sacrifices (Pesahim 109a).  Nowadays, in the absence of sacrifices, we experience the joy of the festivals with “what is appropriate: wine for men, clothing and jewelry for women, and snacks for children.”

The claim that the pleasure of Shabbat should include meat eating also falls on closer analysis.  (R. Nachman Levine tells me that the late Lubavitcher Rebbe quoted his father to the effect that there is no requirement to eat meat on Shabbat in any source. The decisors only mention meat-eating as an example of a possible luxury appropriate for Shabbat. However, one exception: on Shabbat Hazon, failing to eat meat might give the impression of mourning on Shabbat.)

In the rebuilt Temple, however, if the same laws apply as they did in the first two Temples (as Rambam insists they would), kohanim would be required to eat the meat of several varieties of sacrifices, and other Jews would have to eat the meat of the Paschal sacrifice.  Other Jews would also have occasion to eat meat if and when we bring a Thanksgiving offering or a Peace offering (Korban Shelamim). 

I used to ask candidates for conversion if they would eat from the Paschal offering, were the opportunity to arise in their day.  Did their commitment to halakhah outweigh their commitment to vegetarianism?  This, however, remains a highly theoretical question at the present time. 

Themes in favor of vegetarianism also exist in classical Judaism.  A close reading of the biblical text supports the Midrashic observation that Adam and Eve and their descendants were forbidden to eat meat, and the prohibition was lifted only after the family of Noah left the ark. The tradition does not assert that anyone actually followed the law requiring vegetarianism; only that the law demanded vegetarianism.  One could reasonably draw from this Midrash the conclusion that vegetarianism applies in the ideal, Edenic paradise, and that we should look forward to a vegetarian future.

Another support for the picture of Edenic vegetarianism comes from a literal reading of the vision of the prophet Yeshayahu that “the wolf will lie with the lamb,” (11:6) and “the lion will eat grass like cattle” (65:25).

Support for vegetarianism can also come from the prohibition on causing unneeded pain to animals (Tsaar Baalei Hayyim).  The Talmud records a dispute about whether this qualifies as a Torah or rabbinic prohibition (Bava Metsiah 32b; Hulin 115b). 

Despite the prohibition on causing pain to animals, the Torah permits slaughtering animals for food “whenever you feel a strong desire to eat meat” (Devarim 12:20).  Emphasize “whenever,” and this ambiguous phrase seems to mean a general endorsement of eating meat: “whenever you feel like.” Emphasize “avat nafshekah = you have a strong desire” and it seems to mean “only when you feel a kind of lust.” (Errico-Nagar reports that Rabbi Solovietchik took that second approach: you may eat meat only when you have a lust for meat.).

Someone who does not feel a great desire for meat, and does not need meat medically, may not have a need for meat which overcomes the prohibition on causing pain.

Modern factory farms may compound that problem. Simply raising animals under current conditions may qualify as unneeded harm to animals. 

Feeding animals antibiotics to stimulate faster growth may also have health and environmental consequences which have halakhic significance. 

Works Cited
Abravanel, Isaac. Principles of Faith (Rosh Amanah). Trans. Menachem Marc Kellner.  (East Brunswick, NJ; London, Toronto: Associated University Presses, Littman Library, 1982).

Bleich, Rabbi J. David. "Vegetarianism and Judaism," Tradition, Vol. 23, No. 1 (Summer, 1987).

Errico-Nagar, David. “Vegetarianism and Judaism: The Rav’s Radical View” Kol HaMevaser, Feb. 7, 2012.
http://www.kolhamevaser.com/2012/02/vegetarianism-and-judaism-the-ravs-radical-view/

Schwartz, Richard. Judaism and Vegetarianism, Lantern Books, 2001 (New Revised Edition). Thorough analysis of the Jewish case for vegetarianism.  Schwartz has many more publications on this topic.
Shapiro, Marc.  The Limits of Orthodox Theology: Maimonides’ Thirteen Principles Reappraised. (Oxford: Oxford UP, 2004), 8:122-131.
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Zivotofsky, Ari. “What’s the Truth about . . . the Korbanot?” Jewish Action: The Magazine of the Orthodox Union. December 1, 2014.

Do I really have to eat this much matzah?

Have I eaten enough maror (bitter herbs)?

Well, how much matzah do we have to eat in order to fulfill the mitzvah?

One washes one’s hands, and says the blessing “on raising the hands” and takes the matzah in the order in which one put them, the broken one between the two whole ones, and holds them in his hand and blesses “hamotzi” and “on eating matzah” and then breaks the top whole one and the broken one . . . and eats them while reclining, an olive’s bulk of each. If one is unable to eat two olive’s bulks at once, one eats the “hamotzi” first, and then the “on eating matzah.” (Shulhan Arukh, Orah Hayyim 275:1).
The source of this ruling: There is no “eating” with less than a kezayis (equivalent to an olive). (Toras Kohanim, Acharei 12:2; Emor 4:16).

 How fast?
“An olive’s bulk” . . . and the later authorities agree that one only needs to put both olive’s bulks in his mouth at once, and to chew them, but one does not need to swallow them at once, but it suffices to swallow about one olive’s bulk first, and then swallow the other. And even if he swallowed it a little at a time (bedei avad) as long as he did not delay from beginning to end longer than it takes to eat a half loaf (kedei akhilat peras) (Mishneh Berurah note 9)

And how much maror?
After that one takes an olive’s bulk of bitter herbs, sticks it entirely into the haroset, and does not leave it there in order not to weaken the bitter flavor. For this reason one should shake the haroset off it, says the blessing “on eating bitter herbs” and eats it without reclining.
After that one takes the third matzah and breaks it off, and combines it with the bitter herb, and dips it in haroset (Rama: some say we do not dip it, and that is the custom, and so I have seen people do) and says “In memory of the Temple, like Hillel, and one eats them together while reclining. (Shulhan Arukh, Orah Hayyim 275:1).
After finishing the meal each one eats an olive’s bulk of the matzah shemurah from under the tablecloth, in memory of the Pascal sacrifice that was eaten when satisfied (Shulhan Arukh, Orah Hayyim 277:1)
Be’er Heiteiv on the above ruling, note 1: The late rabbis agree that ideally one should eat two olive’s bulks, one in memory of the Pascal sacrifice, and one in memory of the matzah that was eaten with it; but in any event, one must certainly eat an olive’s bulk.

So how big is an olive’s bulk?
According to the OU Guide for Passover 2016 5776:
Rav Chaim Noeh
Kezayit Matzah = 29 cubic centimeters
Kezayit Maror = 19. 3 cubic centimeters
 
Rav Moshe Feinstein
Kezayit Matzah = 43.2  cubic centimeters
Kezayit Maror = 32 cubic centimeters
 
Chazon Ish
Kezayit Matzah = 50  cubic centimeters
Kezayit Maror = 33.3 cubic centimeters

1 cubic centimeter = a bit less than 0.034 ounces.

Maror is a rabbinic mitzvah, when we do not have the Pascal sacrifice, so the rabbis use a more lenient unit for determining the volume of a kezayit. Matzah is a Torah mitzvah even today, so the rabbis use a stricter unit.

However, according to the Mishnah, “the olive that we mention is not a big one, nor a small one, but a medium-sized one, and that is the Agori.”

M. E. Kislev, Dept of Life Sciences, Bar-Ilan University, estimates that the commonly- published sizes for Kezayit is “about ten times greater than the volume of a common fruit olive.” (M. E. Kislev, “An Olive Bulk: The Olive Fruit as an Ancient Unit of Capacity”).

According to Prof. Kislev, Israel now has three distinct varieties of olive, from largest to smallest, Nabali, Souri and Mallissi. He notes that only the Souri, the middle-sized variety has fruit that can remain on the tree through the winter. This fits the description of the Egori olive “Why is it called Egori: Because it keeps its oil while all the others lose their oil. R. Hanina said: all olives, when rains wet them, lose their oil, and this one, rains . . . and it keeps its oil” (Yerushalmi Bikkurim 1:3 on 63, 4)

Archeological evidence shows that ancient Israel used Souri olives, as researchers have found the pits of different varieties at sites in Israel. The ancient Souri olives, based on the pit size, had about 3 cubic centimeters of volume, as do modern Souri olives.

More than a thousand years ago, the Geonim of Bavel were asked about the size of kezayit. (Teshuvot HaGeonim, Harkavy edition. Cited in Kislev “’Kezayit’ Pri HaZayit BeMidat Nofah” 435):
That which you asked about the unit of a large fig, or a medium fig, and so a large olive, a small olive and a medium-sized olive, they are themselves units, and how can one give a unit for the unit? If you suggest it is a unit of weight, our rabbis did not give a precise weight, and the holy One did not require us to be precise with weight, but each one of us will go according to his opinion and fulfill his obligation. We do not need to derive another unit. Rabbi Yehudah says: how do we estimate a medium size? We take the biggest of the big, and the smallest of the small, and average them. Rabbi Yossi says, who will tell us what is the biggest of the big, or the smallest of the small? Rather it all goes according to the opinion of the person who looks.

Also in the responsa of the Geonim appears the notion that the units never appear in weights, since governments can change the weights of their units at will, and who can recover the ancient meaning of the weights. Rather the units come in olives because everyone can see how big an olive is (Slifkin 5).

My wife conducts an informal survey of Jews our age and older by asking, “How much matzah did your grandfather break off for each participant at the earliest seder you can remember?” Invariably people answer by showing a small size, approximately consistent with the bulk of a modern medium-sized olive.

So how did we get to the giant kezayit?

Rambam, Hilkhot Eiruvin 1:9 says that a dried fig is about 1/3 of an egg. The Talmud, Shabbat 91a, says that an olive is smaller than a dried fig. So it follows that the olive is less than 1/3 of the size of egg, according to Rambam (Slifkin 7; see Mishneh Berurah 486:1). Rambam uses a chicken egg as his unit of measurement in the entire Mishneh Torah (Hilkhot Shabbat 8:5).

A Spanish rishon, Rashba, gives the size of an egg as much more than four olives. Another Spanish rishon, Ritva, says that a dried fig is the size of several olives. His olive is thus about 1/9 of an egg, at the upper limit (Slilfkin 8).

A statement in the Talmud (Keritot 14a) asserts that the human gullet holds no more than two olives. Another statement, (Yoma 80a) asserts that the human gullet holds no more than one egg. How do these two statements relate to each other?

Tosafot (on Hulin 103b “Halko Mebahuts”) proposes that a kezayit equals half a chicken’s egg in volume (I have seen the claim that Tosafot means a dove’s egg, which would make his measure close the Rambam’s less than 1/3 of chicken egg.) The two measures fit together perfectly. The composers of Tosafot, living in what is now Northern France and Germany, probably did not have experience with actual olives, which may have made the proposal seem plausible.

Rabbi Joseph Soloveitchik replied to a student: “K’zayis? How big is a k’zayis? I don’t know. But I know a k’zayis is according to most rishonim is a chatzi beitzah (half and egg) and according to [Rambam} is one shlish of a beitzah (third of an egg), and I know that elephants don’t lay eggs.” (Holzer 185). 

We do not have excellent archeological evidence for the size of eggs in the ancient and medieval world. Unlike olive pits, eggs do not keep. Kislev believes that chickens in the Greek-Roman period were about the size of modern Leghorn chickens, and so he estimates the size of a chicken egg in the Greek-Roman period as about 57.6 cubic centimeters. If so, the estimate in Tosafot would have a kezayit at a huge 28.8 cc.

Kislev proposes a different resolution to the two estimates of the size of the gullet. Perhaps we cannot swallow more than two hard items of about 3 ccs, such as olives or hard candies, in one gulp, but we can swallow a much larger soft item, such as an egg (perhaps a raw egg?) (Slifkin asserts that Rabbenu Tam made this same point in a Tosafot on Eiruvin 82b).

Shulhan Arukh Orah Hayyim 486 states: “The amount ‘kezayit,’ some say is half an egg.” Usually, Shulhan Arukh uses the expression “some say” after stating the more definitive position. Here, he leaves “half and egg” unchallenged. Perhaps he feels it superfluous to mention the definitive position, that a kezayit is the same size as an olive.

In Talmud Pesahim 109a, when asked about revi’it required for the cup of wine on Pesah, Rav Hisda rules “the revi’it of the Torah is two fingers by two fingers to the height of two fingers and half finger and a fifth.”

Rav Steinsaltz reports that the unit, “a finger,” gets measured across the thumb at the widest part of the thumb.

Rabbi Yehezkel Landau (1713-93) measured this size in cubic thumbs, according to the Talmud in Pesahim (120a), and compared that with the measure of volume given in eggs. The numbers did not match. He concluded that the eggs of ancient Israel must have been twice the size of modern eggs, for it seemed impossible that thumbs had grown. If so, we should double our measures for all mitsvot related to volume of eggs.

One of his students maintained that Rabbi Landau himself was a tall man, and had broad thumbs. According to R. Frank, Rabbi Landau set the width of a thumb at 2.4 centimeters.

Rabbi Avraham Na’eh set the width of a thumb at 2 centimeters, which yields a revi’it of 86.4 cubic centimeters, extremely close to the size of an average egg and a half (using Kislev’s estimate for the size of a chicken egg, 57.8, then 1.5 eggs equals 86.7 ccs).

Using Rabbi Landau’s measure for the width of thumb, 2.4 centimeters, the revi’it comes to just under 150 cubic centimeters, just about twice as large as a modern egg and a half.

Combine that theory with the conversion table that an olive is half an egg, and one gets the modern Ashkenazi giant kezayit.

Is this enough wine?

The size of the cup should be one Revi’it (a quarter of a log) after it has been mixed with water (Rama: if one wishes to mix it) and one should drink most of it or all of it. If it has many Revi’yot, as many people may drink from it as it has Revi’yot. Some say one must drink most of the cup even if it has many Revi’yot. (Rama: and one must drink this amount without much interruption in between) (Shulhan Arukh Orah Hayyim 272:9).

“Without much interruption” That means he must not delay from the beginning to the end more than the time it takes to drink a Revi’it . . . Magen Avraham writes that if he delays longer than the time it takes to eat half a loaf (kedei akhilat peras) he has not fulfilled his obligation and must return and drink (Be’er Heiteiv note 13).

A Revi’it. But how much is a Revi’it?

According to the OU Guide for Passover 2016 5776: 
Rav Chaim Noeh – 3 ounces
Rav Moshe Feinstein – 3.3. ounces
Chazon Ish – 5.3 ounces

One ounce = just a little less than 30 cubic centimeters.

The amount of a Revi’it is 1½ eggs. If we take Kislev’s estimate for the volume of an egg at 57.8 cubic centimeters, then a Revi’it has to be somewhat under 3 ounces.

Notice all the difficulties in estimating the average size of a chicken’s egg under modern conditions. The eggs that we see in the supermarket do not represent a random selection of eggs. Smaller eggs get made into powder or otherwise diverted from the consumer market. If we have a good way to estimate the modern egg, that may serve as our unit. If we decide to use the ancient egg as our unit, how can we extrapolate with any confidence to the size of ancient eggs?

How long does “as long as it takes to eat half a loaf” take?

Rambam describes a “peras” as 3 eggs, half the standard loaf of six eggs. As long as it takes to eat half a loaf thus means the amount of time it takes to eat a piece of bread with the volume of three eggs.
Rashi rules that a “peras” means 4 eggs. I have seen the claim that these are dove eggs rather than chicken eggs, in which case his unit essentially agrees with Rambam. I have not found a source to substantiate that claim. Even if his unit is chicken eggs, the period in which we are to consume our matzah or drink our wine remains constricted.

Does as long as it takes to eat a half loaf mean, when one is speed-eating, or does it mean, when one is enjoying a leisurely lunch?

Finally, in practice: 

For a sick or elderly person who has trouble eating that much, we should rely on the minimum amounts. The olive’s bulk of matzah should equal about enough matzah to make a life size-statue of a medium size-olive. The olive’s bulk of maror should contain about enough lettuce to make a life-size statue of a medium-size olive. The cup of wine should hold a small revi’it, about 3 fluid ounces.
A healthy person, who has built up an appetite during the long section of the Haggadah retelling the story, and who wants to do the mitzvah with enthusiasm, should eagerly eat more than a mere olive’s bulk (or two, where the authorities recommend that), but this person has no need to try to bolt the food down as fast as possible. One should eat at a reasonable pace, like a person enjoying the bounty of the Giver of all blessing, and like a person enjoying the experience of becoming sanctified by performing a commandment.

Secondary Sources

Frank, R. Yitzhak. The Practical Talmudic Dictionary. Jerusalem: Ariel, 1994, 1991.
 
Holzer, R. David. “Insights from the Rav on the Seder,” The Medieval Haggadah Anthology Jerusalem: Holzer Sefarim, 2014.

Kislev, M. E. “An Olive Bulk: The Olive Fruit as an Ancient Unit of Capacity” in M. Heltzer and D. Eitam. Olive Oil in Antiquity: Israel and the Neighbouring Countries from Neolith to Early Arab Period. Conference, 1987, Haifa.

Kislev, M. E. “’Kezayit’ – Pri HaZayit BeMidat Nofah” Tehumin 10, 5749. 427-437.

Slifkin, R. Natan. “The Evolution of the Olive: The Halakhic History of the Expanding Kezayis.”
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Steinsaltz, R. Adin, A Reference Guide to the Talmud. New York: Random House, 1987. 

In Mishnaic times, Josephus reports on the existence of several other strains of Judaism besides the Pharisees. The Talmud also records several different factions, some included, some excluded. Talmudic rabbis can disagree – on almost every page—but they remain in. Other groups did not:

Samaritans (Kutim) have an intermediate status in the Mishnah, but the Talmud largely counts them as out (Hulin 6a).
Beotheans and Saducees (Tsedukim) count as sectarian Jews.
Minim, unspecified sectarians, populate the Talmud.

In Geonic times and thereafter, the followers of Anan ben David (8th century), later called Karaites, present a serious alternative to Rabbinical Judaism. Rabbinic and Karaite Jews coexisted in several communities in North Africa, Asia and Europe.

The Cairo Geniza contained several ketubot, marriage documents which specify that the rabbinite husband shall not interfere with his wife’s observing according to Karaite halakhah.

Rav Saadia Gaon (882-942) wrote against the Karaites, and instituted acts to separate the Rabbinic Jews from the Karaites. In much of his writing against the Karaites, he marshals arguments against specific Karaite doctrines, such as their denial of the value of the Talmud, their refusal to use fire on Shabbat, their insistence on setting the calendar by observation, their permitting Pesah to begin on any day of the week, and beginning Shavuot always on a Sunday.

Rambam (1135-1204) did not favor separatism. He wrote that the Karaites ‘should be treated with respect, honor, kindness and humility as long as they do not slander the authorities of the Mishna and Talmud. They may be associated with, one may enter their homes, circumcise their children, bury their dead and comfort their mourners.’ (Responsa of Rambam) He recommends treating Karaites with friendship, in the hope that they will return to the source of strength, the Torah They are like “captive children,” raised to believe what they believe through no fault of their own (Laws of Rebels 3:3) Wine remains kosher if a Karaite handles it, according to Rambam: this defines Karaites as Jews in good standing.

Shulhan Arukh does not mention a limit on marriage with Karaites (Even HaEzer 4). Radvaz explicitly encourages such marriages (1:73).

Rama, in his commentary on Shulhan Arukh, does not permit one to marry a Karaite, since their process for divorce differs from ours, they are “doubtful mamzerim.” According to Rama, we also do not accept penitent Karaites who wish to rejoin rabbinic Judaism. (Even HaEzer 4:37).

Other rabbis have permitted intermarriage with Karaites by invalidating their marriages – the witnesses never count – so they are unlikely to become mamzerim. Still others permit intermarriage with other explanations (Teshuvot Noda BeYudah)

In the 1600s: Sabbateans. Followers of Shabtai Tsevi (1626-1676). Mystical, messianic leader, attracted wide followership even among learned Jews and rabbis. Some rabbis excommunicated Shabtai Tsevi at the height of his success. When he converted to Islam (under duress from the leader of the Ottoman Empire) some of his followers remained Jews, but kept their beliefs secret. Most communities accepted former Sabbateans back.

In the 1700s: Hasidim. Followers of Rabbi Yisrael ben Eliezer, the Baal Shem Tov (1698–1760). Early responses to Hasidism raised crucial debates on the mystical doctrine of Tsimtsum, divine contraction to make room for creation provided fuel for split. Hasidic strictures in ritual slaughter threatened to divide the observant Jewish world into two also drove the split. Rabbi Elijah, the Gaon of Vilna, excommunicated followers of Hasidic doctrine.

Reform: In 19th century Germany, governments supported religious communities. As the Reform movement grew, some communities became majority-Reform, but retained more traditional synagogues as well. Rabbis generally opted to head the synagogue in a majority-Reform community; for example, Rabbi Azriel Hildesheimer in Berlin. In Frankfort, Rabbi Shimson Rephael Hirsch took the dramatic step of separating from the Jewish community, and appealing the government for status as a separate faith community.

Rabbi Hirsch noted that proponents of reform called their more traditional co-religionists “Orthodox.” Later, in the mid-19th century, traditional Jews took up the name Orthodox for themselves. The name does not have a history in classical Jewish texts.

In the late 19th century: the rabbis who broke from the Reform movement proclaimed themselves “Conservative” and founded the Jewish Theological Seminary. The relationship between this new movement and Orthodoxy remained complex for decades.

In the early 20th century, issues that defined and split Orthodoxy included moving the reading platform to the front of the synagogue, putting a clock in the synagogue, celebrating weddings in the synagogue, delivering sermons in the vernacular, and maintaining the partition between the men’s and women’s sections. Mehitsah became the defining issue in the mid-20th century.

In “Kol Dodi Dofek,” (1956) Rabbi Soloveitchik identifies two different covenants which tie Jews together. In the “covenant of destiny” (brit yi’ud), we choose to observe halakhah. In the “covenant of fate” (brit goral) we willingly self-identify as members of the people, and so, whether we will or not, share the fate of oppression and persecution.

Developing this dichotomy, Rabbi Soloveitchik permitted cooperation with non-Orthodox Jews on matters relating to the fate of the Jews, while keeping away from discussions based on our commitment to halakhah.

Consistent with this teaching, the Rabbinical Council of America permitted representation on the Synagogue Council of America, along with Reform and Conservative rabbis.

Agudas Yisrael issued a total ban on joining with non-Orthodox rabbis, because joining would appear to grant legitimacy to non-Orthodox Judaism. That argument seems more plausible when Liberal movements in Judaism make up a tiny percentage of the population. When halakhically-observant Jews make up a minority, then perhaps we do not have to worry about granting legitimacy.

In the mid-1950s, Rabbi Soloveitchik negotiated with Rabbi Saul Lieberman at the Jewish Theological Seminary to develop a Beit Din for conversions that would accept candidates who studied with Conservative teachers, and confer conversions according to Orthodox standards. Some characterized this as a joint Beit Din. The negotiations fell through. During the negotiations, Rabbi Moshe Feinstein and several Rashei Yeshivah connected with Agudas Yisrael issued their prohibition on any cooperation with the Conservative movement, and this may have contributed to the collapse of the negotiations.

Rabbi Feinstein published opinions in which he explicitly invalidates all conversions and marriages performed by Conservative rabbis. Rabbi Feinstein in this way rules that thousands of American Jews cannot fall into the status of mamzer. When I studied in Yeshiva, beginning 50 years ago, people believed that Rabbi Feinstein would endorse the conversions performed by specific rabbis of Conservative synagogues, those known to him to observe halakhah to his standards.

Rabbi Soloveitchik maintained the commitment never to enter a Conservative or Reform synagogue. He befriended the Rabbi Joseph Shubow, rabbi of a local Conservative synagogue, Temple Bnai Moshe in Brighton, MA. Invited to co-sponsor a testimonial dinner in honor of his friend, and of the dedication of the new Temple building, Rabbi Soloveitchik sent a letter praising his “dear friend” Rabbi Shubow, but declining, because the Temple would have mixed seating (letter of May 5, 1954 to Philip Fleisher). The label “Conservative” did not appear in his letter; he objected to mixed seating. When Rabbi Shubow died, the funeral took place at that synagogue, and Rabbi Soloveitchik showed his respect, not by attending the funeral, but by standing outside of the synagogue.

Rabbi Eliezer Cohen followed the same policy as Rabbi Soloveitchik. Though Rabbi Cohen vigorously encouraged Orthodox Jews to attend the Intercongregational Men’s Club Dinner, and he himself attended those dinners even when they were held in the social halls of non-Orthodox synagogues, he made it his policy not to enter those synagogues on other occasions. In my last conversation with Rabbi Cohen, I challenged him about that policy. I asked him about how non-Orthodox synagogues differ from the many Orthodox institutions that teach a version of Judaism which he decried. He explained he kept away from organizations that permit what the Torah forbids.

It seems obvious that, according to the Agudas Yisrael standard, we should not call non-Orthodox rabbis by the title “rabbi.” Some Haredi sources put the title in quotation marks. Rabbi Feinstein, in Igrot Moshe, provides a variation on this theme. He refers to Orthodox rabbis with the Hebrew word, “rav.” He refers to Conservative rabbis with a transliteration of the English word, “rabbi.”

A certain student began to attend Rabbi Soloveitchik’s class after receiving ordination at the Conservative Jewish Theological Seminary, where he then taught Hebrew language. When the registrar asked about this student’s right to attend class, and Rabbi Soloveitchik discovered the student’s history, he accepted the student has his own personal admit, and insisted on calling him “Rabbi Kirschenbaum.” Rabbi Aaron Kirschenbaum (1926-2016), later the editor of “Dinei Yisrael,” a leading journal of Mishpat Ivri, non-ceremonial Jewish law.

Rabbi Aharon Lichtenstein told his Talmud class (in 1970 or 71) which included me, that, appearances do the contrary, haredi rabbis are closer to us than Conservative or Reform rabbis, because we share crucial matters of belief with the haredi rabbis. My son Yoel informs me that in his later years Rabbi Lichtenstein did not make this claim. In Mevakshei Panekha, a series of interviews with the novelist and Talmud teacher Haim Sabbato, Rabbi Lichtenstein rejected a complete break with liberal Jewish movements. “Can anyone imagine that we would be stronger without them?” Commenting on Rav Hirsch’s separatism, Rav Lichtenstein says “Today I believe that separatism is simply not realistic. It is not realistic in practical terms and in essential terms” (149).

"So long as we are in the position of power and influence, we can never give recognition to the Reform [a catch-all phrase that in haredi parlance means all of the non-Orthodox Jewish movements]. Although they are Jews, they will not get any recognition. In Judaism there is only one stream – the religious path of Moses and Israel,” R. Aryeh Deri, who is also chairman of the Sefardi haredi Shas Party, said, according a report on the radio interview published by Arutz Sheva.

Yeshiva University School Partnership, under Orthodox auspices, is in the process of merging with the Schechter Day School Network of the Conservative movement, Day Schools of Reform Judaism of the Reform movement, the Jewish Community Day School Network of nondenominational schools, and Partnership for Excellence in Jewish Education. Torah U Mesorah, whose leaders affiliate with Agudas Yisrael, has not joined the merger. On a policy level, Torah U Mesorah opposes coeducation of boys and girls, and so remains separate from Orthodox co-ed schools; Torah U Mesorah certainly also opposes joining with other movements of Judaism.

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Sephardic Leader Calls Western Wall Deal “Horrible” – Compares Reform Jews to “Dogs.”
Forward JERUSALEM Feb. 4, 2016— A former head of the Shas Sephardic Orthodox party slammed the Israeli Cabinet’s approval to expand the egalitarian section of the Western Wall, joining several politicians who have ridiculed the deal and liberal movements of Judaism.
“This is a horrible disaster and an attack on the Holy of Holies,” Eli Yishai said in an interview Thursday with Army Radio. “The next thing we’ll see is Reform Jews putting tefillin on dogs and calling them up to the Torah.”
Moshe Gafni, a haredi Orthodox lawmaker who chairs the Israeli Knesset’s powerful Finance Committee, said he would not recognize the decision and called Reform Jews “a group of clowns who stab the holy Torah.”
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Rabbi Saul Berman, in a 1999 interview with then rabbinical student Josh Yuter
Edah does not have a position on the question of the relationship to the Conservative and Reform movements. We don’t engage in dialogue; it’s not our mission to do so. On the other hand, we are committed to the proposition that it is important for us to sustain a relationship to the Conservative and Reform movements that emerges from the mitzvah of Tochaha. That is I don’t believe that it is useful to stand on the street corners and condemn Conservative and Reform Jews. I believe that it is important for them to understand where we stand. And they do. I mean there is no doubt in the mind of the Conservative and Reform rabbis as to where Edah stands as an Orthodox organization on questions of patralineality, on the impermissibility of homosexual intercourse or on the question of gitten. On the other hand, we believe that it is possible for us to make greater progress in moving them in relation to these issues by maintaining a kind of relationship with them that is expressive of what is necessary in Tochaha, which means Tochacha yotzeit meahava. When Tochacha emerges from love, when they know that there is a loving concern on our part for their well being as Jews, then there is a possibility of movement. If they believe that we simply hate them and have dismissed them from the Jewish people, then anything that we say is irrelevant to them, and then we don’t fulfill the mitzvah of Tochacha at all.
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​So what options do observant Jews have today?

We could consider one who does not observe ritual halakhah (according to our understanding of halakhah) as a willful sinner; leaders deserve condemnation, and followers we should ostracize as bad influences on our children.

We could consider the non-observant Jews (according to our understanding of halakhah) as misguided, in classical terminology, each one as “tinok shenishba” a captive child, who never had the opportunity to learn Torah. According to this stance, leaders of non-halakhic Judaism deserve condemnation, but we should deal kindly with ordinary Jews, until we can draw them close to observance. Hazon Ish, R. Avraham Yeshaya Korelitz (1978-1953) employed this terminology.

Rabbi Norman Lamm (born 1927) opposed the distinction between leaders and followers: even the leaders of other streams of Judaism could qualify as “captive children.”

We could treat them with respect, considering that they have accomplishments that we must recognize from a pure Torah perspective. Rav Avaraham Yitzhak Kook (1865-1935) stressed that that non-observant Jews who built the Jewish community in Israel accomplished tremendous mitsvot, not less significant than the accomplishments of Jews who kept Shabbat and kashrut.

We could recognize that non-observant Jews, and Jews who observe according to different standards, include a great multitude, many people with the most admirable values and the highest accomplishments, some, sadly, not so admirable. Rabbi Lichtenstein wrote “I do not want to judge this whole community, nor am I able to do so. . . . If we had to grant a certificate of rectitude we would have to judge the whole person . . . as they do in schools, that give one mark in one subject, and a different mark in another. In some ways they are like thorns in our eyes, and in others, they have values and accomplishments in some specific areas that I only wish we could match” (Mevakshei Panekha 143).

This insight applies even in Torah. Bible scholar and Conservative Rabbi Jacob Milgrom (1923-2010) once helped me through public recitation of a Psalm at a house of mourning. I had trouble reading the text in small print and dim light (my excuse) and he helped me from memory. Nehama Leibowitz quotes liberal Rabbi Benno Jacob.

In practice . . .

Ibn Rushd (1126-1198), known in the West as Averroes, distinguishes between two types of disagreement. I can disagree with you and argue that the facts do not support your position, or I can disagree with you and argue that you do not belong in our organization any longer. The Muslim thinker considers that the argument about the facts has intellectual content. I can learn something from listening to your opinions respectfully, and answering them with my own reasoning. The argument about belonging has no intellectual content. It just represents social pressure.
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According to R. Jonathan Sacks, the Jewish thinker Rabbi Shelomo Luria, known as Maharshal (1510-1573), quotes ibn Rushd by name, and approves of his analysis of the two ways of disagreeing. Rabbi Sacks also approves of this approach.