Eruvin 9 and 10 Eruv principles- לבוד and פס ארבע

One of the most important rules regarding מחיצות (partitions) is the principle of לבוד.

The Gemara (Eruvin 4b) told us that this rule is הלכה למשה מסיני (see post on that daf.)

It states that any gap in partitions less than 3 טפחים in width is considered as if it is closed.

This has major ramifications both in the laws of Eruvin and of Sukkah.

It is necessary, however, to formulate exactly what the precise mechanism and scope of this rule is.

Let us suggest two possibilities for now:

  1. A gap that is less than 3 טפחים wide is not considered a gap at all, under any circumstances
  2. A gap that is less than 3 טפחים wide is still considered a gap, but it is the type of gap that is negligible enough to be ignored regarding certain מצוות.

If the first, objective definition is used, then it is irrelevant whether the gap’s effect is significant in practise or not, it simply does not count as a gap but is considered closed.

In contrast, according to the second formulation, there could be certain situations where such a gap is not negligible, and we do not disregard it.

In practise, it seems impossible to claim that such a gap has no noticeable effect on the partitions. It certainly lets in air from the outside, as well as insects and many smaller or medium sized animals that can get through the space. It also allows people to see inside, certainly no small thing.

As such, if the purpose of the partitions was meant to protect against the elements, keep small animals out, or create visual privacy, this rule seems highly illogical.

If, on the other hand, the purpose of the partitions is to demarcate the boundaries of a private domain, or keep larger animals out, then it makes sense that so long as the partitions are dominant and gaps are negligible, the partitions should still be valid.

At the bottom of the previous daf, the Gemara discussed a case where the beam is placed on two pegs protruding outwards from the public facing side of the existing walls of the מבוי.

As such, the beam is not on top of the מבוי, but the internal length of the beam is in contact with the walls.

Rav Chisda rules that the law depends on an earlier dispute we saw regarding the way in which the beam acts as a partition.

According to the opinion that normally permits one to carry underneath the beam, because we view the outside edge of the beam as the partition (as if it continues downwards to the ground,) this beam will be invalid, seeing as the outer edge is not in contact with the walls. Even though the beam might be only a טפח wide, and the gap between the outer edge and the walls should thus be viewed as “closed” due to the principle of לבוד, Rashi explains that seeing as this is not a real partition (but just a conceptual halachik construct) the leniency of לבוד does not apply.

According to the view that it is forbidden to carry underneath the beam because the inner edge of the beam forms the imaginary partition, in this case it will be permitted, seeing as the inner edge of the beam is in direct contact with the walls.

At this point, we already see that the rule of לבוד is not absolute but is limited to certain cases. After all, if it was absolute and a gap of less than 3 is never considered a gap at all, then it should apply even where the mechitzah is not real but only a halachik construct.

Rava holds that even according to the view that the imaginary partition is formed by the inner edge of the beam, this beam is not valid, seeing as it is not physically on top of the מבוי itself, something he requires.

Rav Ada bar Ahava objects on the basis of a beraisa that rules that if the beam is משוכה or תלויה less than 3 טפחים (or 4 טפחים acc רשב”ג) from the walls of the מבוי, it is sufficient due to the rule ofלבוד .

He understands that משוכה refers to when the beam is not directly over the מבוי but placed on pegs protruding outwards, as in the case we have been discussing.

He understands תלויה as referring to a case when the beam is suspended directly over the מבוי, but not directly over the walls of the מבוי- instead, it is supported by a reed placed in the middle of the opening and does reach the actual walls.

If the former assumption is correct, we see that there is no requirement for the beam to be physically on top of the מבוי, as claimed by Rava, and there also seems to be no limitation in the rule of לבוד that precludes it from being applied to another halachik construct such as an “imaginary” partition.

The Gemara answers that both the term משוכה and תלויה could be referring to a case when the beam is supported by a reed and doesn’t reach the wall but is still suspended directly over the מבוי.

The former term refers to a beam that reaches the walls of the מבוי on one side, whereas the later term refers to a beam that doesn’t not reach the walls on either side.

In both cases, the rule of לבוד makes it as if the beam reaches the walls.

However, in a case where the beam itself is not directly over the מבוי, לבוד does not help.

The Gemara explains that both these cases are needed, as we might have thought that the rule of לבוד can only be applied once, on one side, but not twice.

Once again, we see that the rule of לבוד is not a blanket rule, but has its limits- in this case, the Beraisa teaches us that both cases are within its limits, but if it did not have some limits, this would unnecessary.

Rav Ashi fails to see a significant distinction between applying the rule of לבוד on one side or on both sides, but says the Beraisa is referring to one case where the beam is both משוכה AND תלויה- thus removed both horizontally and vertically from the walls of the מבוי . In such a case, the rule of לבוד renders the horizonal gap ineffective and the rule of חבוט ( a different halachik construct whereby we view the edge of the beam as if it continues downwards till the walls) closes the vertical gap .

There is much to discuss regarding why the rule of לבוד isn’t used also for the vertical gap, and why the rule of חבוט is limited to only 3 טפחים, and Tosfos and other Rishonim go into this further, but for our purposes, the Gemara explains it was not a foregone conclusion that the rule of לבוד can be used in combination with another halachik construct like חבוט, and we needed the Beraisa to tell us that it can be.

We see from here also that the rule of לבוד was not seen as absolute by default but can have its limitations. To what extent the Beraisa has taught that that these limitations are not as great as we might have thought, or whether it has taught us that there are no limitations at all and that the rule of לבוד is indeed absolute, is still open for further analysis.


The rule of לבוד is applied once again at the bottom of 9b, in a discussion that flows over onto our new daf.

Here, we have been dealing with a case where a smaller courtyard opens on one side into a larger courtyard.

The walls that close the extra length of the outer courtyard can be seen from the larger courtyard, and the larger courtyard is thus not considered completely open on one side.

Seeing as the gap between the smaller and larger courtyard is less than 10 טפחים, it is considered as a valid entrance and the larger courtyard is considered sufficiently enclosed to carry inside it.

In contrast, the gap between the two courtyards forms the entire fourth side of the smaller courtyard, and as it is completely open, even a gap of less than 10 טפחים wide needs to be closed somehow.

Yet Rabbah bar Rav Huna has already concluded that נראה מבחוץ ושוה מבפנים (where the לחי used to close the fourth side of the מבוי can be seen from outside but not from inside) is permitted. Seeing as when viewed from the outside, the opening does not appear to take up the entire side, the smaller courtyard should also be fine as is.

The Gemara answers that we are dealing with a case where the sidewalls of the smaller courtyard extend into the larger courtyard, blocking the excess width of the shared wall from being seen from “outside” (the part of the larger courtyard that is opposite the smaller one.)

The Gemara asks that seeing as we are dealing with a larger courtyard that is no more than 1 Amah wider than the smaller one, there should be less than 3 טפחים between the side walls of the larger courtyard and those of the smaller one, and the rule of לבוד should effectively close this gap, making the whole area permitted.

It answers that we are dealing with a case where the smaller courtyard is not placed symmetrically in the middle of the larger one, but rather with a gap of 2 טפחים between its sidewalls and those of the larger courtyard on one side and 4 on the other.

Even though the rule of לבוד applies on the one side, it does not apply on the other, and according to the view of Rebbe who requires a courtyard completely open on one side to be marked on BOTH sides, the opening is still a problem.

This takes us into new territory entirely.

Until now, we have dealt with a מבוי that is closed on three sides but completely open on one side. מדרבנן it is forbidden to carry inside it until a post is placed on either side or a beam from one side to the other.

We already saw earlier that this does not apply to any area enclosed on 3 sides, but just to any area that has the very specific properties of a מבוי :

  1. At least 2 courtyards (with 2 houses each) opening to it
  2. Its length (2 closed sides) is greater than its width (one open and closed side.)

Today we see that a courtyard, which does not meet these qualifications, is treated more strictly, and according to Rebbe, needs to be partly closed on both ends of the open area, even if it is less than 10 אמות wide (if it is more, this might not even be sufficient.)

This has major ramifications for private front-yards and gardens, which we started discussing earlier in our post on daf 5, and I hope to be able to focus on this more as the discussion comes up in the Gemara.

Eruvin 5 The unfenced courtyard and a mathematics teaser


We have learnt that although מדאורייתא (biblically,) an area enclosed on three sides is generally considered a רשות היחיד (private domain) as far as the laws of carrying on shabbos are concerned, there is a rabbinical requirement to mark or enclose the fourth side in some way.
 
It is important to note that the biblical rule could have both stringencies and leniencies associated, a subject I hope to discuss in a later post.
 
The leniency is that at least on a biblical level, one is permitted to carry within this area, or from this area to an adjacent private domain, without restriction.  The stringency is that if one carries from this area to a public domain, one would be liable for biblical level shabbos desecration, with all its ramifications.
 
The rabbinic requirement to enclose or mark the fourth side limits one’s ability to carry within that area or from that area to the adjacent רשות היחיד  without doing so, but probably does not affect the biblical prohibition against carrying from it to the רשות  הרבים.   
 
Until now, we have focused on a מבוי, or narrow street, which requires only a לחי (pole) or קורה (beam) to mark the fourth side.
 
What happens with an unfenced private front-yard or garden, either belonging to the owners of one house, or shared by various houses?
 
Does this also need to be enclosed, and if so, is the solution that works for a מבוי also sufficient for such an area?
 
On the one hand, this area is less public than a מבוי and more similar to a private domain by its nature, so perhaps Chazal didn’t see the same need to make it more distinguishable from the public domain.
 
On the other hand, it still shares an open fourth side to the public domain, or at least to a כרמלית ( open area not busy enough to be a public domain, but treated by Chazal with the stringencies of both public and private domains.)
 
On this daf, we see that there are strict rules defining the מבוי  that may be permitted by just a לחי  or קורה . Otherwise, it is considered a חצר (courtyard) and is actually treated more stringently!
 
1.       Its width needs to be narrower than its length, the width being the dimension only enclosed on one side, as opposed to the length which is the dimension enclosed on both sides.
2.       It needs to have houses and courtyards open to it. The Gemara (Shabbos 130b and Rashi) understands the later to mean at least two courtyards that each have two houses open to them.
 
As such, it seems clear that both a shared courtyard and a private one certainly do not meet the later criteria, and might sometimes not meet the former one either.
 
It seems to follow from here that at least the shared courtyard would definitely be treated stricter than the מבוי, and with the argument in favor of leniency for a less public area to be treated more leniently disregarded, in the absence of precedent to  the contrary , it seems that this would also be the case with a private front-yard or garden.
 
What precisely is required in order to be able to carry in such an area will hopefully be the topic of a later post as the sugyos develops.

 
There is a מחלוקת (dispute) on this daf between Rav Yosef and his student, Abaya regarding the minimum length of a מבוי.
 
Rav Yoseif holds that 4 טפחים (handbreadths) are sufficient, whereas Abaya requires 4 אמות (arm-lengths.)
 
Abaya attempts to prove his point from the above rule that we learnt- in order to be considered aמבוי  as far as the more lenient requirement for a לחי  or קורה, there have to be at least 2 courtyards that open to it.
 
As the minimum width of a פתח  (opening) is 4 טפחים  (the maximum being 10 אמות,) it is impossible for a courtyard to share one with a מבוי  that itself is only 4 טפחים long, without the entire length being open and thus disqualified .
 
The opening can also not be along the width that is already closed, as the width may not be wider than the length!
 
Rav Yoseif counters that one opening could still be possible on each side, if it is in the corner between the length and the width.
 
Rashi explains that this could be made of a 3 טפחים  gap along the length PLUS a 1 טפח  opening along the adjacent wall of the width, making the minimum 4 טפחים in total.
 
Tosfos , as well as other Rishonim make the rather strong observation that Rashi is not being precise, as the true entrance would then be marked by the diagonal between the enclosed part of the length and the enclosed part of the width, which mathematically (by pythagorus) will be the root of 10, still below the minimum width of 4 טפחים  !
 
Is Tosfos accusing Rashi of being unaware of basic mathematics such as the theorem of Pythagoras? Absolutely impossible, as there are various sugyos which mention this, approximating the root of 2 with 7 over 5 (See sukkah 8a for example)
 
It is also very simple for any mathematical layman to measure such a diagonal and see that the diagonal is much closer to 3 than 4.
 
As such, it seems clear that Tosfos understood that Rashi was aware of this discrepancy but deliberately chose to ignore it and be happy with an approximate minimum with  slightly more than 3 in place of 4, something that seems rather odd.
 
We have seen elsewhere that the Tosfos have pointed out that Chazal themselves were not always precise with their measurements (see Eruvin 13b for example) , but this was a question of rounding to the nearest integer, not rounding down more than a  half  and resulting in a major leniency.
 
It thus seems more likely that Rashi did not measure the entrance from the diagonal, but from the imaginary wall that would exist in the corner if the 3 plus 1 handbreadths were closed.
 
This would be a rather substantial מחלוקת  with a huge נפקא מינה (practical ramification) regarding the status of the area in-between this imaginary boundary and the diagonal as well as whether a bent opening like this is valid.
 
It is also clearly not the way Tosfos understood Rashi!
וצריך עיון גדול

These posts are intended to raise issues and stimulate further research and discussion on contemporary topics related to the daf. They are not intended as psak halacha.