Category Archives: Conversion

Follow-up #3

Last week we discussed Tosafot Yebamot 47a’s presentation of Rabbeinu Tam’s apparent position that many people are presumptively Jewish, meaning that if they claim to be Jewish, halakhic authorities will believe them without requiring corroborating evidence.  According to a beraita on Yebamot 47a, the claim to be a convert is believed only with corroboration or if there is a prior presumption.  Rabbeinu Tam commented that this is true only if there is prior knowledge of Gentileness; someone coming literally out of nowhere and claiming to be a convert would be believed.

Rabbeinu Tam (or perhaps Tosafot on his behalf) cited as proof a story from Pesachim 3b, in which a Gentile was given a portion of a Passover sacrifice simply by showing up.  He addressed an implicit challenge to his proof: what if that story was not based on presumption, but rather on the probability that most people presenting themselves to eat the sacrifice are Jewish?  He responded that most people presenting themselves as Jewish are also Jewish, so Pesachim and Yebamot remain parallel.

However, this response muddies the waters – do we believe the claim to be Jewish because of a presumption, or rather on the basis of probability?  We explained last week that presumptions (chazakah), unlike probability claims (rov),  can exist even without an evidentiary basis,.

Tosafot cite the beraita on Yebamot 47b we looked at two weeks ago as a second proof for Rabbeinu Tam.

מעשה באחד שבא לפני רבי יהודה,

ואמר לו:

נתגיירתי ביני לבין עצמי.

א”ל רבי יהודה:

יש לך עדים?

אמר ליה: לאו.

יש לך בנים?



א”ל: נאמן אתה לפסול את עצמך, ואי אתה נאמן לפסול את בניך.

A case: Someone came before Rabbi Yehudah,

and said to him:

“I converted when I was alone”.

Rabbi Yehudah said to him:

“Do you have witnesses?”

He said: “No.”

“Do you have children?”


He said to him:

“You are believed to disqualify yourself, but you are not believed to disqualify your children.”

At first glance this text seems to contradict rather than support Rabbeinu Tam: why don’t we presume the convert to be Jewish?  Tosafot, however, start the other way around: why do we presume the children to be Jewish, so that eliminating the father’s testimony leaves their identity legally solid?[1]

ועוד ראיה משמעתין,

דאמר ליה ר”י אי אתה נאמן לפסול את בניך,

There is another proof (for Rabbeinu Tam’s position) from our own sugya,

where R. Yehudah says to him “You are not believed to disqualify your children”,

Why isn’t the father presumed Jewish?  Tosafot answer that in fact he is, but a technical mechanism nonetheless prevents him from enjoying all the privileges of Jewish status.


ואיהו גופיה כשר, אלא דשוי נפשיה חתיכה דאיסורא,

אבל אם בא על בת כהן – לא פסלה,

כדפי’ לעיל.

And he himself is also valid, just that ‘he has made himself a slice of prohibition’,

but if he were to have relations with a daughter of a kohen[2], he does not disqualify her,

as I explained earlier.

The simplest explanation of this mechanism is that it functions in the same manner as an oath.

The upshot of Tosafot is that we presume the father to be Jewish even though he has told us that he is not by claiming to have been invalidly converted.  Here the basis for treating the father as Jewish cannot be probability – no one thinks that most people claiming not to be Jewish are actually Jewish.  Rather, the basis must be presumption.

The last section of Tosafot notes that a story on Yebamot 45a should not be seen as evidence for Rabbeinu Tam.  As background for this story, you need to know that the Talmud records three positions as to the status of matrilineals:

a) that they are mamzerim

b) that they are invalid to marry kohanim

c) that they are no different than Jews with two Jewish parents.


תלמוד בבלי מסכת יבמות דף מה עמוד א

ואף רב יהודה מורה בה להיתירא,

דכי אתא לקמיה דרב יהודה, א”ל: זיל איטמר, או נסיב בת מינך.

וכי אתא לקמיה דרבא, א”ל: או גלי, או נסיב בת מינך.

Rav Yehudah also ruled to permit (a matrilineal Jew to marry a Jew with two Jewish parents),

as when (a matrilineal Jew) came before Rav Yehudah, Rav Yehudah said to him: “Go hide, or else marry a woman like yourself (i.e. matrilineal)”,

and when he came before Rava, Rava said to him: “Either go into exile, or else marry a woman like yourself (i.e. matrilineal)”.

Prima facie, Rav Yehudah and Rava suggest that the matrilineal simply show up in a Jewish community elsewhere, where he will be presumed (in their opinion, correctly) to be a halakhically valid marriage partner for Jews born from two Jewish parents, even where he would be socially ineligible would his heritage be known[3].  This suggests that the new community will not investigate their claim to be Jewish.

Tosafot argue, however, that the new community might have investigated whether he was Jewish, but not have researched his family.  Once again, we are left to wonder how he could prove his Jewishness without revealing his parentage.  Bottom line, though, this explanation is offered only to reject using the beraita as a proof for Rabbeinu Tam; once Rabbeinu Tam has triumphed anyway, there is no reason to assume the new community checked at all whether he was Jewish.

ומההיא דלעיל (דף מה.) דא”ל זיל גלי אין ראיה,

דשמא לא היו בודקים אלא אם הוא ישראל אם לאו, אבל במשפחתו לא היו בודקין.

From that earlier (narrative” in which he says to him “Go into exile” there is no proof (for Rabbeinu Tam),

as perhaps they would only investigate whether he was Jewish, but they would not investigate his family.


[1] The text does not actually say that the children are considered Jewish, only that their father’s testimony does not determine their status, but Tosafot presumes that they are considered Jewish.

[2]I would emend based on parallels to “a woman whose halakhic status would change as the result of having sex with a Gentile”

[3] This is not the right place to discuss the ethics of hiding one’s background from potential spouses, the current social status of matrilineals in the Jewish community, or the relationship of this passage to the issue of mekach taut as a method of freeing agunot.

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Follow-up #2

The 2013 SBM Sh’eilah which you received two weeks ago focused on a woman whose Jewishness comes into question as the result of a conversation with her daughter.  It might reasonably be thought that if the mother cannot be declared Jewish, the same is automatically true of the daughter – but such is not the case. Last week we explained how it be halakhically possible to rule that a woman was not Jewish but and simultaneously that her daughter was Jewish, as follows:

If Robin (the mother) is disqualified on the basis of her own testimony, and Catherine (the daughter) would be considered Jewish if we disregard her mother’s testimony, we may well be able to treat Catherine as Jewish even if we treat her mother as not Jewish.

We then added:

In practice, what evidence could Catherine have for her Jewishness other than being Robin’s daughter?  This of course raises the question of how one establishes one’s Jewishness, and whether and under what circumstances there is a presumption of Jewishness.  This discussion as well relates to a dispute between Rabbi Yehudah and his colleagues, as well as a number of fascinating Talmudic narratives, and I look forward to sharing at least some of those with you next week.

Let us move on to that discussion.

On Yevamot 46b-47a the following fascinating but enigmatic beraita appears:

מי שבא ואמר גר אני, יכול נקבלנו?

ת”ל: אתך –

במוחזק לך.

בא ועדיו עמו, מנין?

ת”ל: וכי יגור אתך גר בארצכם.

אין לי אלא בארץ, בח”ל מנין?

תלמוד לומר. אתך

בכל מקום שאתך;

אם כן, מה ת”ל בארץ?

בארץ – צריך להביא ראיה, בח”ל – אין צריך להביא ראיה,

דברי ר’ יהודה;

וחכמים אומרים:

בין בארץ בין בחוצה לארץ – צריך להביא ראיה.

  1. One who comes and says “I am a ger=convert” – one might have thought we accept him –
  2. so Scripture teaches: “with you” –
  3. only if you already presume him to be.
  4. If he comes with his witnesses, from where do we know?
  5. Scripture teaches “If there should gar with you a ger . . . “.
  6. “. . . in your land” –
  7. So far I only know in the land – from where do I know (that this is also true) in the diaspora?
  8. Scripture teaches “with you” –
  9. wherever he is with you.
  10. If so, why does Scripture teach us by saying “in (the) [your] land”?
  11. In the land – he must bring evidence; in the Diaspora – he need not bring evidence,
  12. according to Rabbi Yehudah.
  13. But the Sages say:
  14. Whether in the land or in the diaspora – he must bring evidence.



We can ask many basic questions about this beraita, such as:

What is the definition, or: what are the boundaries, if any, of the “acceptance” referred to in line 1?

Is the presumption in line 3 of born Jewishness or rather of conversion?

Why do we need a Torah text to teach me that witnesses are believed?

How does ““If there should gar with you a ger . . . “ teach that one believes a claim of conversion supported by witnesses?

What is the basis of the dispute between Rabbi Yehudah and the Sages?

These questions are asked by the Talmud and Rashi, and we may return to them in future weeks.  The question that matters to us this week, however, is this:

The first line, at least in the opinion of the Sages, asserts that a claim to be a convert rather than a Gentile is believed only if there is a prior presumption supporting the claim.  Is this also true of a claim to be a born Jew?

Rabbeinu Tam, as cited in the Tosafot to Yebamot 46b, asserts that the claim to be a born Jew is accepted as is.  He in essence reverses the beraita by arguing that the prior presumption of conversion is necessary only when there is evidence of prior Gentileness; a person with no known background would be believed if they claimed to be Jewish.  Rabbeinu Tam asserts this on the basis of the following beraita from Pesachim 3b.

ההוא ארמאה דהוה סליק ואכיל פסחים בירושלים.

אמר: “כתיב (שמות יב) ‘כל בן נכר לא יאכל בו’, ‘כל ערל לא יאכל בו’, ואנא הא קאכילנא משופרי שופרי!”

אמר ליה רבי יהודה בן בתירא: “מי קא ספו לך מאליה?”

אמר ליה: “לא.”

“כי סלקת להתם, אימא להו: ‘ספו לי מאליה.'”

כי סליק, אמר להו: “מאליה ספו לי.”

אמרו ליה: “אליה לגבוה סלקא!”

אמרו ליה: “מאן אמר לך הכי?”

אמר להו: “רבי יהודה בן בתירא.”

אמרו: מאי האי דקמן?  בדקו בתריה ואשכחוהו דארמאה הוא, וקטלוהו.

שלחו ליה לרבי יהודה בן בתירא: “שלם לך רבי יהודה בן בתירא! דאת בנציבין ומצודתך פרוסה בירושלים.”

A Gentile would go up and eat from Paschal sacrifices in Jerusalem.

He said: “Scripture writes ‘No gentile may eat it”, “No uncircumcised my eat it”, and yet I eat from the best of the best!”

Rabbi Yehudah ben Beteira said to him: “Did they feed you from the tail?”

He replied: “No”.

“When you go up there, say to them: ‘Feed me from the tail.’”

When he went up, he said to them: “Feed me from the tail.”

They said to him: “The tail goes to the Most High!”

They said to him: “Who said this to you?”

He replied: “Rabbi Yehudah ben Beteira.”

They said: What is this before us?  They investigated his background and discovered that he was a Gentile, and executed him[1].

They sent to Rabbi Yehudah ben Beteira: “Peace unto you, Rabbi Yehudah ben Beteira!  For you are in Nezivin but your net is spread in Jerusalem.”


Here is Rabbeinu Tam’s argument as presented by Tosafot:

תוספות מסכת יבמות דף מז עמוד א

במוחזק לך –

  1. אומר רבינו תם:
  2. דדוקא בדידעינן דהוה עובד כוכבים מעיקרא,
  3. דאי לא הוה ידעינן, מהימן, מגו דאי בעי אמר ‘ישראל אני’, דמהימן,
  4. כדמשמע בריש מסכת פסחים (דף ג: ושם)
  5. גבי ההוא עובד כוכבים דהוה סליק ואכיל פסחים בירושלים.
  6. ואין לומר
  7. שאני התם דהוו סמכי ארובא דהוו ישראל,
  8. דהא בכל מקום נמי איכא רובא, דרוב הבאין לפנינו בתורת יהדות ישראל הם!?
  9. ועוד ראיה משמעתין,
  10. דאמר ליה ר”י אי אתה נאמן לפסול את בניך,
  11. ואיהו גופיה כשר, אלא דשוי נפשיה חתיכה דאיסורא, אבל אם בא על בת כהן – לא פסלה, כדפי’ לעיל.
  12. ומההיא דלעיל (דף מה.) דא”ל זיל גלי אין ראיה,
  13. דשמא לא היו בודקים אלא אם הוא ישראל אם לאו, אבל במשפחתו לא היו בודקין.

“Only if you already presume him to be” –

1. Says Rabbeinu Tam:

2.  (The requirement that a convert have a prior presumption applies) specifically when we knew that he was originally a Gentile,

3. because if we had not known, he would be believed (when he claimed to be a genuine convert), since he has a migo[2] that he could have said ‘I am a Jew’, as someone who makes such a claim is believed,

a. as is implied at the beginning of Pesachim

b. regarding the Gentile who came and ate the Pesach in Jerusalem (that he was initially able to do so suggests that anyone claiming to be Jewish was accepted until counterevidence emerged).

c. and it would be incorrect to (reject Rabbeinu Tam) and say

d. that  because they relied on the majority (of those who presented themselves to eat the Pesach) being Jewish, (whereas our beraita discusses a non-Passover case in which no such majority exists),

e. because everywhere else there is also a majority, (namely) that most of those who come before us בתורת יהדות=presenting themselves as Jews are Jews!?

Rabbeinu Tam argues, as best I can tell, that it is obvious from the story that in previous years no one had investigated whether the Gentile was Jewish before feeding him from the Passover sacrifice, and this indicates that generally a claim to be Jewish was presumed true.

Tosafot then raise a possible objection to the generalization: Perhaps it is not that the claim to be Jewish is believed, but rather that the claim to be eligible to eat the Passover is believed, on the ground that most people making such a claim are telling the truth?  In other words, perhaps there is no general presumption of Jewishness, just a situational probability analysis.

Tosafot’s response is that most people claiming to be Jewish are Jewish, so one does not need the presumption ever.

Here we need to clarify the difference between presumption (חזקה) and probability (רוב).

A presumption can exist without a ground – it can simply be a default setting.  For example, Jews are presumed to be telling the truth when they act as formal witnesses in beit din – they have a chezkat kashrut – simply by being born, even if they are born into a culture that has made lying into a fine art.

A probability, by contrast requires a ground – we need to understand what we are claiming, why we think it is likely true.  Determining the context of the odds is vital.  For example – suppose most of the people in the world are not Jewish, but most of the people claiming to be Jewish are – does the majority support someone’s claim to be Jewish, or oppose it?  Should we seek more precise sociological data – for example, see whether either majority is affected by skin color, age, or level of education?

Note also that handling conflicts between presumption and probability is a massive topic.

Note also that halakhah likely often requires one to investigate ordinary probabilities to see if one can determine the status of a particular case, and allows one to presume that an individual case came from the majority only if either further investigation is impractical, or else if there is a superprobability (likely somewhere between 85 and 95 percent.)

Some practical questions for us then are

1)      If we accept as normative the position of Rabbeinu Tam as recorded by Tosafot – what is the probability today that those who claim to be Jewish actually are Jewish?  Do the percentages vary geographically, eg among Israel, Russia, and the US, in ways that we must account for halakhically?

2)      Does Rabbeinu Tam’s migo argument apply for someone who claims to be a convert and was not previously known to be Gentile, but whose previous Gentileness could be discovered easily, eg. via a Google search?

3)      Does Rabbeinu Tam’s claim that a claim to be Jewish is accepted presumptively apply even if the person making the claim has not previously identified as Jewish, or had previously identified as not Jewish, and so had, before making the claim, been assumed to be not Jewish?

Next  we will discuss Tosafot’s second proof for Rabbeinu Tam, as well as a disproof Tosafot reject.


[1] It is not a capital crime for a Gentile to eat the Passover, so presumably there is a backstory about the particular gentile – perhaps he was a spy?

[2] An argument of the form:  If I were lying, I would have made a stronger claim than this, and you would have believed me – so believe me when I make this weaker claim.

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