Separating Conjoined Twins: Part III - Tereifah & Rav Moshe Feinstein’s Ruling by Rabbi Chaim Jachter

Editors’ note: To read the first two parts of this series, visit the Halachah Files section on the Kol Torah website,


In last week’s issue of Kol Torah, we delved into Rav Moshe Feinstein’s understanding of Rodeif and his theory on the effect relative degrees of pursuit have on the determination of the proper Halachic course of action for specific cases of Rodeif. In this week’s issue, we present Rav Bleich’s synthesis of Rav Moshe’s conceptualization of Rodeif with his conjoined twins ruling.

Rav Bleich’s Explanation of Rav Moshe’s Ruling

Rav Bleich argues that the same reasoning of relative degrees of pursuit applies to the case of the conjoined baby sisters.  The sisters were unequal pursuers since the right-side twin had no chance of survival for more than a year even if the left-side twin were to be sacrificed. The left-side twin, however, had a very reasonable chance of survival if the other twin were to be sacrificed.  The right-side twin’s life expectancy is regarded as only Chayei Sha’ah and is viewed as a Tereifah while the right-side twin enjoyed the possibility of achieving a normal lifespan.

Thus, the baby twin girls could be construed as “unequal pursuers”, since the left-side baby pursues only Chayei Sha’ah whereas the right-side baby is pursuing one with a possibility to live a normal lifespan.  It follows that the right-side twin is a qualitatively greater Rodeif than the left-side twin and thus the right-side twin may be sacrificed in order to save the left-side baby.  Thus, Rav Bleich offers a cogent explanation for Rav Moshe’s ruling. Just as Rav Moshe in 1935 (Teshuvot Igerot Moshe Y.D. 2:60) permitted the sacrifice of one shul in order to save the rest of the city’s shuls from the hands of the Soviet communist government, so too he permitted (or even required) the sacrifice of the right side twin to save the other twin.

One the other hand, Rav Yaakov Kaminetsky might have rejected the analogy between the situation of the twins and that of the pregnant woman because the inequality between fetus and mother is far greater than the gap between the twins.  The difference between the mother who is classified as alive and the fetus who constitutes only potential life is a qualitative and fundamental difference, as opposed to the twins, who both constituted a full life (although one is a Teriefah and the other is not).  I thank Rav Chaim Schertz zt”l of Harrisburg, Pennsylvania for providing this insight.

Rav Kaminetzky could have also disagreed with Rav Moshe’s explanation of Reish Lakish’s opinion.  Thus, Rav Moshe’s approach works only according to Rabi Yochanan.  Rav Kaminetzky then might have agreed with Rav Bleich’s opinion that we have no basis upon which to follow Rabi Yochanan over Reish Lakish.

Rabi Akiva Eiger and Teshuvot Panim Me’irot

Rabi Akiva Eiger (to Ohalot 7:6) cites Teshuvot Panim Me’irot who suggests that Ein Dochin Nefesh Mipnei Nefesh, the principle that “we do not push one life aside for another”, applies only when the one of the two endangered people would survive in any event.  However, if both would die absent intervention, then it might be permissible to kill one to save the other.

According to this suggestion it is permissible to kill the right side twin to save the left side twin since both would have perished if left alone.  However, as Rav Bleich notes, this is insufficient basis to act, since both the Panim Me’irot and Rabi Akiva Eiger conclude “Tzarich L’Hityasheiv BaDavar”, the matter requires further deliberation.

Are the Twins Deemed to be a Tereifah?

The assumption that an infant lacking a heart or possessing a congenitally malformed heart is a Tereifah requires clarification. An obvious source for that position is the eighteenth-century ruling of Rav Yonatan Eibeschutz in a celebrated controversy between himself and Rav Zevi Ashkenazi (the Chacham Zvi).

A young woman soaked and salted a chicken, but failed to find a heart. She consulted the Chacham Zvi who ruled (Teshuvot Chacham Zvi, nos. 74, 76 and 77) that the animal was kosher. Chacham Zvi reasoned that, since it is impossible for any creature to survive without a heart for even a brief period of time, it must be assumed that the chicken, which had thrived and developed in a normal manner, must indeed have been endowed with a heart. The absence of a heart, declared Chacham Zei, must be attributed to the predatory nature of a cat which must have been in close proximity. Not content with simply ruling with regard to the case presented to him, Chacham Zvi further announced that "even if witnesses will come and testify that they saw with open eyes that nothing was removed from the body of the chicken, it is certain that their testimony is false for it is contrary to reality."

In sharp disagreement, Rav Yonatan Eibeschutz, Kereti u-Peteti 40:4, declared that the testimony of credible witnesses cannot be dismissed peremptorily but rather "it must be assumed that there was some piece (of tissue) which does not appear as a heart but which is designed to fulfill the functions of the heart, but yet the chicken is Tereifah since it is not a normal heart." Thus, Kereti u- Peleti clearly regards an animal born with an anomalous heart to be a Tereifah because it lacks a normal heart. However, Chazon Ish     (Yoreh De’ah 4:14) takes issue with Kereti u-Peleti in arguing that the chicken thus described is indeed kosher. Chazon Ish argues that, although removal of the heart does indeed render the animal a Tereifah, there is no source for a ruling that an anomaly of the heart similarly renders the animal a Tereifah.

Moreover, there is no indication that Kereti uPeleti would regard a six-chamber heart in the same light as a mere piece of tissue that fulfills the functions of a heart. The dispute between Chazon Ish and Kereti u-Peleti occurs in the context of the status of an animal. Rambam (Hilchot Rotzei’ah 2:8) asserts that the Talmudic enumeration of the various Tereifot is exhaustive. However, insofar as human Tereifot are concerned, Rambam asserts that, in every era, the particular anomalies that render a human being a Tereifah are to be determined in accordance with the medical knowledge of the day. Thus Rambam rules that a human being is not to be considered a Tereifah (and his murderer must be executed) unless "it is known with certainty that this (person) is a Tereifah and the physicians declare that this wound has no cure in a human being or he will die as a result of it unless something else kills him (sooner)." Rambam's categorical statement regarding medical assessment of human Tereifot indicates both that a wound or anomaly that would render an animal a Tereifah does not necessarily render a human being a Tereifah, and also that a wound that will cause death in man renders a human being a Tereifah even though, with regard to animals, it is not one of the enumerated Tereifot.

There are indeed many Rishonim who disagree with Rambam's position and maintain that the determination of status as a Tereifah in humans is no different from determination of that status in animals. For a list of those authorities see Encyclopedia Talmudit, XXI, 4-7 and Nishmat Avraham, Yoreh Dei’ah 29:1, note 1. Nevertheless, Rambam's position together with the view expressed by Kereti u- Peleti with regard to anomalies of the heart might provide a Poseik with ample grounds for a determination that a child born with such a cardiac anomaly is a Tereifah.

The Approach of Ponovich Rosh Yeshiva Rav Dov Povarsky

Briefly, Rav Povarsky wishes to claim that the right side twin is not only a Tereifah but a “Neifel”.  The Gemara (Shabbat 135a) regards a “Ben Chet” (a baby born after only eight months of gestation; it is an example of a Neifel) as “a stone” and thus not alive.  Accordingly, Rav Povarsky argues that one may sacrifice the right side twin since it is not considered to be alive according to the Halacha.

Here is Rav Bleich’s rejection of Rav Povarsky’s approach in brief:  The right side twin is not a Neifel since it has lived more than thirty days.  See Rav Bleich’s article for an in-depth presentation.  

LeChatchilah Ein Morin Kein

The Rambam (Hilchot Yesodei HaTorah 5:5) notes that even if the designated person satisfies the requirement of deserving to die, similar to Sheva Ben Bichri, nonetheless “LeChatchilah Ein Morin Kein”, initially this instruction is not conveyed to them.  The basis for the Rambam is the following story related by the Talmud Yerushalmi:

A man named Ula Bar Kushav was sought by the Roman authorities for some unnamed crime. He fled to Lod, then (the early third century CE) an important city in Judea with a large Jewish population. The Romans surrounded the city and demanded that the Jewish community turn over Bar Kushav. If he were not turned over, the Romans would raze the entire city.

The leading rabbinic authority in the city at the time was Rabi Yehoshua ben Levi , known both as a Halachic expert and as a mystic. In accordance with the opinion of Rabi Yochanan, he sought out Bar Kushav, “placated him, and turned him in,” thereby saving his city and its thousands of Jewish inhabitants.

Rabi Yehoshua ben Levi had been accustomed to receive regular visits from the Eliyahu HaNavi, but in the wake of this incident the visits ceased. Rabi Yehoshua imposed upon himself several fasts in order to induce Eliyahu to reappear to him. Eliyahu HaNavi reappeared, but just to say: “You expect me to reveal myself to a Moseir (informer)?” Rabi Yehoshua ben Levi replied that he had acted in accordance with a rabbinic law. Eliyahu replies “But is that the law of a Chasid?”

The aforementioned Bi’ur HaGra notes that this Yerushalmi is the basis for the Rambam ruling in favor of Reish Lakish over Rabi Yochanan.  The Gra challenges this since Eliyahu HaNavi merely states that this is not Mishnat Chasidim, the actions proper for a spiritually high level individual.  However, the essential Halacha follows Rabi Yochanan.  Moreover, Ein Lemeidin Min HaAgadot, as we mentioned earlier, Agadic episodes do not constitute an authoritative source.

Rav Yaakov Kaminetzky could respond to Rav Moshe that he never should have instructed the family to consent to this surgery, following the Rambam.  Rav Moshe could respond that the Rama, Gra and Taz do not cite this episode in the Yerushalmi and do not say LeChatchilah Ein Morin Kein.  Rav Yaakov, though, could note that both the Shach (Yoreh Dei’ah 157:15) and the aforementioned Chochmat Adam do rule in accordance with the Rambam that Lechatchilah Ein Morin Kein.


Rav Moshe’s ruling was implemented in practice by Dr. Koop and the right-side twin was sacrificed in order to save the life of the left-side twin.Sadly, the left-side twin died a few weeks later not due to complications from the surgery but due to contracting hepatitis B from a blood transfusion. Although the loss of both of these precious children constitutes an enormous tragedy, a bit of a silver lining in this very dark cloud is the great Kiddush Hashem and honor of Torah generated by the enormous respect Dr. Koop accorded to Rav Moshe Feinstein and his ruling.May the study of Rav Moshe’s ruling serve to honor and elevate the Neshamot of these two dear young infants.

Sechirat Reshut: Part I - The Implementation & Challenges of Sechirat Reshut in the Modern Age by Rabbi Chaim Jachter

Separating Conjoined Twins: Part II - Rav Moshe’s Position on Rodeif & Relative Degrees of Pursuit by Rabbi Chaim Jachter