Combat Exoskeletons on Shabbos

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imageby R. Gil Student

I. Bionic Men

Reports, albeit somewhat dubious, are circulating regarding Russian development of combat exoskeletons that can mechanically increase the strength and endurance of soldiers. Worn like body armor, these artificial extensions of the body are expected, within five years, to receive direction through brain waves. When a soldier thinks about moving his arm or leg, the mechanical extension will move, thereby multiplying the soldier’s strength. While combat is almost always a case of life-threatening danger that overrides the rules of Shabbos, the tantalizing reports still raise the question of whether such technology can be used on Shabbos in non-combat situations.

The basic technology already exists. Computers have already been developed that can receive instructions through brain waves. This Brain Computer Interface (BCI) technology currently requires direct contact with the skull but the possibility of remote connection, a sort of brain wifi, is certainly conceivable. I’m hardly an expert so it may already exist and I just do not know about it. I see three questions related to Shabbos with this technology.

First, can we use BCI to perform a forbidden labor? Can I command, through my thoughts, a plow to plow my field or my coffee maker to brew me fresh coffee? Second, can I use this technology to utilize a machine to do something that is not otherwise forbidden, such as turning the page in a book or lifting a fork full of food? (We’ll get to the third question at the end of this essay).

II. Thinking Labor

Rav Shlomo Zalman Auerbach was asked this question, apparently multiple times. He believed that there is a Talmudic precedent for prohibiting an activity on Shabbos that is done through thought (beyond thinking about business and similar thoughts, which is a separate issue). R. Zalman Menachem Koren, the editor of Rav Auerbach’s writings on electricity (Me’orei Eish Ha-Shalem, vol. 2 pp. 765-766), discusses Rav Auerbach’s oral response. Rav Auerbach pointed to the prohibition against designating food as terumah, the portion given to priests and forbidden to others, on Shabbos (Tosafos, Gittin 31a sv. be-machashavah). Even an activity that consists of thought can be forbidden.

In one of his earliest writings (Me’orei Eish, ch. 4), Rav Auerbach quotes a responsum by Rav Avraham Walkin (Zekan Aharon vol. 1 no. 15), in which the author argued that someone who miraculously cooks through thought or speech violates a biblical prohibition. Rav Walkin proves this from the man (manna) that the Jews are in the Desert. The Torah (Ex. 16:23) forbids cooking the man on Shabbos. However, the man required no preparation–you merely thought what you want and it tasted that way. Clearly, Rav Walkin argues, cooking through thought is biblically forbidden. Rav Auerbach rejects this entire line of argument (although not necessarily the conclusion) because the Torah only forbids cooking with fire, not miraculous cooking. Whatever you may be doing wrong by thinking man to be cooked, it isn’t cooking.

Rav Yisrael Rosen (Be-Chatzros Beis Hashem, p. 90) writes that he asked Rav Auerbach the same question and received the same answer about designating terumah. However, Rav Rosen challenges this proof. He points out that designating terumah violates the rabbinic prohibition of fixing an object. If so, it is not a Shabbos rule that thought can violate the prohibition but a function of designating terumah. Since the rules of terumah allow thought, the food is “fixed” and the Shabbos rules are violated. There is no general rule here to be extracted that Shabbos can be violated by thought.

Rav Rosen quotes Rav Meir Dan Plotzki (Keli Chemdah, Beshalach) who also attempts to prove from the cooking of the man that a forbidden labor caused by thought is prohibited. However, Rav Auerbach’s above objection should apply similarly. Rav Plotzki also gets philosophical. He points out that on Shabbos, we rest like God did after creating the world. Since God created the world through thought, a labor that is caused by thought is also forbidden. Although one can counter that God created the world through speech, it is not clear to me whether divine speech and divine thought are distinct.

III. Miraculous Labor

Rav Rosen briefly raises the idea that performing a forbidden activity through thought is comparable to performing it using supernatural powers. For example, killing someone by invoking God’s name or writing by asking a question of the Urim Ve-Tumim. If directly causing a labor by speaking is allowed, then certainly causing it by thinking is permitted. Rav Shay Schachter advances this argument in a recent lecture, citing many more examples. He quotes a responsum by Rav Chaim Palaggi (Lev Chaim, vol. 2 OC 188), in which the author permits extinguishing a fire on Shabbos supernaturally (with a segulah), such as reciting Psalm 98.

I believe his father, Rav Hershel Schachter, implies such a position in an article. In Be-Ikvei Ha-Tzon (p. 47), the senior Rav Schachter writes in regard to gerama and what is required for an act to be forbidden on Shabbos:

אף דבעינן מעשה האדם, לאפוקי שוא״ת ומחשבה, מכ״מ כח גברא לא בעינן

Even though we need a human action–as opposed to sitting doing nothing and thinking–we do not need human power

Maybe I am overreading this brief phrase but I think it might permit otherwise forbidden activities caused by thought.

IV. Natural Labor

However, Rav Asher Weiss (in an online essay, perhaps from his book on Exodus), rejects the comparison to miracles offered by the younger Rav Schachter. Rav Weiss argues that miraculous and supernatural actions are inherently different from natural causation. A supernatural activity is really caused by God, not man, and therefore is permitted. But when a person directly causes a forbidden activity, even if just by thinking, then it makes sense to say that he has effectively pushed the plow himself.

However, lacking a definitive proof, Rav Weiss hedges, saying that at best causing a forbidden activity by thinking constitutes gerama, which is rabbinically forbidden except in exigent circumstances. He concludes that whether this constitutes direct or indirect labor requires more study, but it is definitely forbidden under normal circumstances.

V. Extended Human

However, this discussion only answers the first question: can you use thought to perform a forbidden action? Regarding an electronic prosthetic limb, the issue turns to whether you may use thought to move an electronic device. It is not entirely the same for two reasons:

First, electronic motion may be only rabbinically prohibited. Second, and perhaps more importantly, the device itself might be considered part of the person, which brings us to the third question: what is the distinction between a person and the machines he uses? Some today argue to an extreme that your computers are an extension of your own mind. More moderate thinkers suggest that artificial appendages become part of you. Is a hearing aid distinct from you? A pacemaker? An artificial heart? If an artificial limb is considered part of you, then you may use it on Shabbos like you use your arm.

Personally, I’m a simple man and look at the issue simply. If it’s organic then it is part of you, even a donated organ and even if grown in a laboratory. If it is inorganic, even partially, then it is not part of you. If and when they make completely organic computers, then maybe that can become part of you, as well. I am not a halakhic authority so my conclusions are tentative and should not be followed. But it would seem that this line of thinking implies that artificial body parts that violate rabbinic Shabbos prohibitions (absent the considerations of thought, discussed above) may only be used by someone who would otherwise be defined as ill but not life threatening. Similarly, artificial body parts that violate biblical prohibitions may only be used by someone who would otherwise be in a life threatening situation. I am not aware what halakhic authorities have said on this subject. (In short, the Bionic Man is assur according to some authorities.)

When it comes to exoskeletons, we have to ask whether they are external to the human body. If they are, as I suggest, then we arrive at the dispute above. According to Rav Shlomo Zalman Auerbach and Rav Asher Weiss, they are forbidden. According to Rav Shay Schachter and possibly his father, Rav Hershel Schachter, this might be allowed (I did not hear the younger Rav Schachter reach a definitive conclusion). Rav Rosen also seems to lean toward leniency but does not reach a final conclusion.

About Gil Student

Rabbi Gil Student is the Editor of, a leading website on Orthodox Jewish scholarly subjects, and the Book Editor of the Orthodox Union’s Jewish Action magazine. He writes a popular column on issues of Jewish law and thought featured in newspapers and magazines, including The Jewish Link, The Jewish Echo and The Vues. In the past, he has served as the President of the small Jewish publisher Yashar Books and as the Managing Editor of OU Press. Rabbi Student currently is serving his third term on the Executive Committee of the Rabbinical Council of America and also serves as the Director of the Halacha Commission of the Rabbinical Alliance of America. He serves on the Editorial Board of Jewish Action magazineand the Board of OU Press. He has published four English books, the most recent titled Search Engine volume 2: Finding Meaning in Jewish Texts -- Jewish Leadership, and served as the American editor for Morasha Kehillat Yaakov: Essays in Honour of Chief Rabbi Lord Jonathan Sacks.


  1. One type of cardiac pacemaker senses the rate of the atria and paces the ventricles accordingly. When an individual engages in physical activity, his atrial rate will naturally increase, and the pacemaker will sense this and pace the ventricles at the higher rate. Based on what you wrote, are there any authorities who would prohibit an individual with such a pacemaker from engaging in any activity that would increase his heart rate (which is virtually all activity), since this would necessarily result in an increased frequency of electrical activity by the pacemaker?

  2. MiMedinat HaYam

    we have a quasi miraculous fire known as ‘toldot ha’chama’ i.e., cooking by sunlight (i believe the case is boiling an egg using sunlight) which is permitted deoraita, prohibited derabban.

  3. Great Post!
    I’m not sure I understand Rav Shlomo Zalman’s inference from the Tosfos in Gittin. Tosfos is not even discussing the possibility of Truma by thought on Shabbos, Tosfos is discussing why hafrashas truma is asur at all on Shabbos, it should be mutar since efshar bemachshava, so actual hafrasha is not considered a tikun. (And the answer is a distinction between tevel and meduma.) But nowhere does Tosfos actually address truma bemachshava on Shabbos, so I don’t see how you can infer from Tosfos that it’s asur bemachshava. (If anything I would infer the opposite…) Anyone with any thoughts?

    The Mishnas Yaakov (R Yaakov Rosenthal, Dayan of Haifa) seems to learn the Tosfos as I did, that there is no issur of hafrasha on Shabbos bemachshava, and seems to indicate that the rashash learned the same way.

    I would add that I believe your diyuk in Rav Schachter’s language is correct; see eretz Hatzvi #6 where he discusses at length that Melacha on Shabbos requires a maase. However, he distinguishes between melachos and gezeiros, and posits that gezeiros can be violated passively (shev veal taase.)

    If so, it could be that violation of Shabbos via thought would depend on whether the particular issur is a melacha or a a gezeira. (This may be a reason to prohibit Hafrashas Teruma bemachshava on Shabbos, because Rambam cites two reasons for the issur, one is kemetaken and one is kemakdish, which I believe is asur bc gezeira shema yichtov. If so, then the issur hafrasha could be violated passively, since it is a gezeira. It’s a stretch to explain Tosfos this way (if you believe Tosofos prohibits hafrasha bemachshava) because Tosfos seems to indicate that the problem is metaken and not makdish.)

  4. My take is that the sources are so far removed from this reality that a clear micro-halachic argument could be made that it’s permitted but it clearly should be forbidden until such time as it becomes a part of society (like refrigerators) and then will have no choice but to permit.

  5. I’m no rabbi, just a techie, so my Halachic “input” here is non-existent. Here is a technical data-point that might greatly COMPLICATE the issue, or make it MUCH simpler:

    In these more advanced “bionic” systems coming out today, that are directly responsive to the user, there is typically NO THOUGHT involved. Rather the sensors are responding to changes in muscle tension or electrical charges in the muscles or nerves*. So such an artificial limb (or exoskeleton) would be in motion BEFORE your decision to move, reached a conscious level – Just the way we ALL function daily. No-one [normal] makes a decision to move each leg, rather they think ‘Walk’. But even that thought is typically registered in the brain, after the body has already engaged the processes to do so. It is these processes that the artificial limb is responding to, not the much later thought.

    So this issue could, possibly, either:
    1) L’chumra – make the action identical to that of a natural limb.
    2) L’Kula – make any such usage G’ramah d-G’ramah.

    An example that is accessible to the general public is the Segway, the two-wheel “vehicle”. When you want to stop, your body automatically tenses up, changing your balance. It is that change, that the vehicle’s sensors responds to.

    • We need to define thought. Some have argued that what you state means we have no free will, only ex post facto rationalizations.

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