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It is rare but possible for conjoined twins to remain alive and healthy into adulthood, such as is the case with Abby and Brittany Hensel. They have distinct sets of heads, hearts, and lungs. They have two arms and legs and a shared reproductive system. One can be asleep while the other is awake. They have distinct personalities, desires, and opinions.

Suppose there were a set of Jewish conjoined twins in similar circumstances, either male or female. My basic question is this: In terms of halachah, would they be considered one person or two?

There are a range of issues to which this would apply. For example:

  • Would they (as men or women) be permitted to marry, and if so, would they marry one person or two, with one ketubah or two?
  • As men, would they count as one or two for a minyan or zimmun?

What are some other issues that arise from this situation?

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Maybe it matters where they are cojoined. – Daniel Sep 2 '13 at 21:26
Yes, that's part of what I'm wondering. – Cislunar Sep 2 '13 at 21:40
There are probably 1000 other cases you could ask this about. Interesting that you chose these two. (BTW minyan and zimmun are not necessarily parallel here.) – Double AA Sep 2 '13 at 22:11
I had lots of ideas, but I wanted to keep the question as focused as possible. I thought the question of "how many people are they" was the root issue and that these issues exemplified the problem. – Cislunar Sep 2 '13 at 22:21
@Annelise If the twins are considered two separate people, I don't see how marriage would be possible: Besides for the prohibition of marrying one's wife's sister in her lifetime, yichud would be impossible. – NBZ Sep 9 '13 at 14:48

2 Answers 2

.מנחות דף לז

בעא מיניה פלימו מרבי מי שיש לו שני ראשים באיזה מהן מניח תפילין א"ל או קום גלי או קבל עלך שמתא אדהכי אתא ההוא גברא א"ל איתיליד לי ינוקא דאית ליה תרי רישי כמה בעינן למיתב לכהן אתא ההוא סבא תנא ליה חייב ליתן לו י' סלעים איני והתני רמי בר חמא מתוך שנאמר פדה תפדה את בכור האדם שומע אני אפילו נטרף בתוך ל' ת"ל אך חלק שאני הכא דבגולגולת תלא רחמנא

Soncino translation:

Pelemo enquired of Rabbi, If a man has two heads on which one must he put the tefillin?’ ‘You must either leave’, he replied, ‘or regard yourself under the ban’. In the meantime there came a man [to the school] saying, ‘I have begotten a first-born child with two heads, how much must I give the priest?’ An old man came forward and ruled that he must give [the priest] ten sela's. But this is not so! For Rami b. Hama learnt: From the verse. The firstborn of man thou shalt surely redeem, I might conclude that this would apply even when the firstborn was rendered trefah within thirty days [of his birth]. Scripture therefore added, Howbeit, limiting thereby [the general application]! — In this case it is different since the Divine Law declared [the law of redemption] to be governed by the expression ‘per head’.

It would appear that for הלכות that we count specifically the head, siamese twins count as two, but for anything else they count as one.

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How do you get "but for anything else they count as one"? Anyway it's odd, since one of the heads would have emerged first and he'd be firstborn, right? – Annelise Sep 3 '13 at 13:03
it says ''In this case it is different since the Divine Law declared [the law of redemption] to be governed by the expression ‘per head'', leading me to the conclusion that this דין is applicable specifically where there is a גזירת הכתוב, no where else. – moses Sep 3 '13 at 18:14
it also appears that in order for this פסק to work you would need to say אפשר לצמצם, that they can indeed come out as one. if you held אי אפשר לצמצם, the father would probably be חייב only one פדיון הבן. – moses Sep 3 '13 at 18:15

There are a number of halachic issues, for example, the Gemarah in Menachot (page 37) discusses conjoined twins with regard to tefillin, and Piskei Teshuvot 225:20 in name of Sh”t Shevut Yacov 1:4 writes that one may make the blessing of "Meshaneh HaBriyot" on Siamese twins.

The most famous/talked about is the ethical/halachic dilemma of separating twins where doing so can/will do harm (to ''one' of them'). For a list of resources on this topic, see:

For more, see here:

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Welcome to MiYodea! Please include a summary of the links, in case they go dead. – Danny Schoemann Nov 1 at 8:59

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