Rambam - 1 Chapter a Day

[The following rules apply when] there is a window between two courtyards: If the window is four handbreadths by four handbreadths1 or larger and it is within ten handbreadths of the ground - whether it is [almost] entirely above ten handbreadths and only a [small] portion is within ten handbreadths, or it is [almost] entirely within ten handbreadths and only a [small] portion is above ten handbreadths - [an option is granted to] the inhabitants of the courtyards.2

If they desire to join in a single eruv, they may. This causes [the entire area] to be considered a single courtyard, and carrying is permitted from one [courtyard] to the other.3 If they desire, they may make two eruvim, each for [the inhabitants of their respective courtyards]. [It is then forbidden] to carry from one courtyard to the other.]

If the windows are smaller than four [handbreadths by four handbreadths] or the entire window is above ten handbreadths from the ground,4 they may make two eruvim, each for [the inhabitants of the respective courtyard].

When does the above apply? To a window between two courtyards. When, by contrast, the window lies between two houses,5 [they are permitted to make an eruv] even if the window is above ten handbreadths from the ground.6

Similarly, when there is a window between a house and a loft, if the inhabitants desire to establish a single eruv they may, even if there is not a ladder [leading to the window], provided [the window] is four [handbreadths] by four [handbreadths]. If the window is round and it can circumscribe a square that is four [handbreadths] by four [handbreadths], it is considered as if it were square.

When there is a wall or a mound of hay that is less than ten handbreadths high7 between two courtyards, they must make a single eruv and may not make two eruvim. If [the wall or the mound] is ten or more handbreadths high, they must make two eruvim, each for the respective courtyard.

If there is a ladder8 on either side of the wall,9 it is considered to be an entrance, and if they desire, they may establish a single eruv. Even if the ladder is standing upright, next to the wall, and it is impossible to ascend it without moving its lower portion away from the wall, it permits [them to participate in a single eruv]. [Moreover,] even if the top of the ladder does not reach the top of the wall, if there are less than three handbreadths between them,10 it permits them to participate in a single eruv if they desire.

If the wall is four [handbreadths] wide and a ladder is positioned on either side of the wall, they may make a single eruv, if they desire.11 If the wall is not four [handbreadths] wide, and there are less than three handbreadths between the [two] ladders, they may make a single eruv.12 If there are more than three handbreadths between [the ladders], they must make two eruvim.13

[The following rules apply when] one builds a bench14 above a bench at the side of a wall [separating two courtyards]: If the lower bench is four handbreadths [high], [we consider it as if the height of the wall] were reduced.15 If the lower [bench] is not four handbreadths [high], but there are less than three handbreadths between it and the upper [bench], [we consider it as if the height of the wall] were reduced.

[In such situations,] if [the inhabitants of the courtyards] desire, they may make a single eruv. Similar [principles apply] regarding wooden steps placed close to a wall.

[The following rules apply when] there is a high wall separating two courtyards, and a projection16 protrudes from the middle of the wall: If less than ten handbreadths remain from the projection to the top of the wall, one may lean a ladder in front of the projection,17 and [this grants the inhabitants] the option of making a single eruv. If, however, one stands the ladder [against the wall] at the side of the projection, [we do] not [consider it as if the height of the wall were] reduced.18

If the wall is nineteen handbreadths high, [it is sufficient] to have a projection protrude for the inhabitants to have the option of making a single eruv. For there are less than ten handbreadths from the earth to the projection, and less than ten handbreadths from the projection to the top of the wall.19

Were the wall to be twenty handbreadths high, two projections are required for the inhabitants to have the option of establishing a single eruv. [Moreover, the projections] may not be parallel to each other:20 [In this way,] there will be less than ten handbreadths between the lower projection and the ground, and less than ten handbreadths between the upper projection and the top of the wall.

If a date palm is chopped down and inclined from the earth to the top of a wall, the inhabitants have the option of establishing a single eruv.21 It is not necessary for them to make it a permanent part of the structure. Similarly, the [very] weight of a ladder22 causes it to be considered as having been placed permanently; it is not necessary to affix it to the structure.

If [the divider] separating two courtyards is made of straw,23 [the inhabitants] may not make a single eruv although there are ladders on either side. A person will not ascend the ladder, because nothing is supporting it.24 If the ladders are in the center, [leaning on a firm support,] and there is straw on either side, [the inhabitants] have the option of making two eruvim.25

When there is a tree at the side of the wall, and it was used as a ladder for the wall, [the inhabitants] have the option of making a single eruv. [Although] it is forbidden to ascend a tree [on the Sabbath], since the prohibition is only a sh'vut,26 [this does not cause the option to be denied].27

If an asherah28 has been made to serve as a ladder for a wall, [the inhabitants do] not [have the option of] making a single eruv. For ascending [the asherah] is forbidden by the Torah, since one is forbidden to derive any benefit from it.29

[The following rules apply when] a wall is ten handbreadths high, and [the inhabitants] desire [to tear down a portion of the wall] to reduce its height so that they will be able to establish a single eruv. They have the option of establishing a single eruv, provided the portion whose height they reduce is [at least] four handbreadths long.30

If [the inhabitants of one of the adjoining courtyards] tear down a portion [of their side] of the wall so that it is less than ten [handbreadths high], they are granted [permission to use] the shorter portion of the wall.31 The remainder of the wall that is high is divided between [the inhabitants of] both courtyards.

[The following rules apply when] a high wall between [two] courtyards is breached: If the breach is ten cubits [wide] or less, they [still may] establish two eruvin.32 They do, however, have the option of establishing a single eruv, because [the breach] can be considered to be an opening. If [the breach] is more than ten [cubits wide], their only option is to establish a single eruv; they may not establish two eruvin.33

If the breach is less than ten [cubits wide], and one [desires to] make it more than ten cubits, it is necessary to hollow out34a portion of the wall ten handbreadths high.35 [When this is done, the only option remaining is to] establish a single eruv.

At the outset, if one desires to open a breach larger than ten [cubits] in the wall, it is necessary that the height of the breach be equivalent to that of [an ordinary] person.36

When there is a trench at least ten handbreadths deep and at least four handbreadths wide between two courtyards, it is necessary for [the inhabitants] to establish two eruvin.37 If its dimensions are less than this, [the inhabitants] must establish a single eruv; [they] do not [have the option of] establishing two eruvin.38

If the depth of the trench is reduced by [adding] earth or pebbles, [the inhabitants] must establish a single eruv; [they] do not [have the option of] establishing two eruvin.39 For it can be assumed that the earth and the stones were intended to become a permanent part of the trench.40 If, by contrast, one reduced [the depth of the trench] by adding straw or hay, the reduction is not [significant] unless one intends41 that they become a permanent part [of the trench].

Similarly, if one reduces the width [of the trench] with a board or with reeds42 by placing them across the entire length of the trench, [the inhabitants] must establish a single eruv; [they] do not [have the option of] establishing two eruvin.

Any entity that may be carried on the Sabbath43 - e.g., a basket or a cup - is not considered to reduce its depth, unless one affixes it to the earth [firmly], in such a manner that one must dig with a spade to dislodge it.

When one places a board that is [at least] four handbreadths wide across the trench, [the board is considered to be an entrance]. [Therefore, the inhabitants] may establish a single eruv. They also have the option of establishing two eruvin.

Similar [rules apply when] two balconies are positioned opposite each other [across the public domain], and a board is extended from one balcony to the other.44 [The inhabitants] may establish a single eruv. They also have the option of establishing two eruvin, each one for his own balcony.

If the two balconies are on the same side [of the public domain], but are not at the same height - instead, one is higher than the other [the following rules apply]: If they are within three handbreadths of each other, they are considered to be a single balcony45 and [the inhabitants] may establish only a single eruv. If they are more than three [handbreadths] apart, they must establish two eruvin,46 each one for his own balcony.

[The following rule applies when] between two courtyards, there is a wall four handbreadths wide,47 which is ten handbreadths high from one courtyard, and at ground level48 at the second courtyard: The width of the wall is granted to the inhabitants of the courtyard at which it is at ground level, and it is considered to be an extension of their courtyard. [The rationale is] that since it is easily accessible to the inhabitants [of this courtyard], and more difficult to use for [the inhabitants of the other], it is granted to those for whom it is easily accessible.

Similarly, if there is a trench between the two courtyards that is ten handbreadths deep for the courtyard on one side and at ground level for the courtyard on the other side, the width of the trench is granted to the inhabitants of the courtyard at which it is at ground level. [The rationale is] that since it is easily accessible to the inhabitants [of this courtyard], and more difficult to use for [the inhabitants of the other], it is granted to those for whom it is easily accessible.

[The following rules apply when] there is a wall between two courtyards that is lower than the upper courtyard, but higher than the lower courtyard:49 [During the week,] the inhabitants of the upper courtyard may make use of the breadth of the wall by lowering articles to it, and the inhabitants of the lower courtyard may make use of it by throwing articles onto it.

On the Sabbath, the inhabitants of both courtyards are forbidden to use the wall unless they establish a single eruv. If they do not establish an eruv, it is forbidden to bring articles that were left on the breadth of this wall into the homes,50 nor may one bring articles from the homes to the breadth of the wall.

[The following rules apply when there is] a ruin that is a private domain between two houses: If [the inhabitants of] both houses can use the ruin by throwing objects into it,51 each one causes the other to be forbidden to use it [unless they establish an eruv].

If it is easy for [the inhabitants of] one [of the houses] to use [the ruin], while [the inhabitants of] the other may not throw articles into it [easily], because it is deeper than [their domain], it is granted to those who can use it [more] easily.52 They may use it by throwing articles into it.

All the following are considered to be [parts of] a single private domain:53 all the roofs of the city - despite the fact that some are high and some are low - all the courtyards, all the enclosures that were enclosed for purposes other than dwelling and are each less in area than that required to sow two se'ah,54 the breadths of all the walls, and all the lanes [in which one may carry because] either a post or a beam has been erected.

One may carry articles left in one [of these areas] at the commencement of the Sabbath to another without an eruv. One may not, however, transfer articles left in the homes to these areas unless an eruv is made.

What is implied? When an article was left in a courtyard at the commencement of the Sabbath, whether the inhabitants of the courtyards established an eruv for themselves or whether they failed to do so, it is permitted to take the article from the courtyard to the roof or to the top of the wall. Afterwards, it may be taken from the roof to another roof adjacent to it, even if [the second roof] is higher or lower than it.

From the second roof, it may be taken to another courtyard, and from the other courtyard to a third roof in a third courtyard. From this courtyard, it may be taken to a lane, and from the lane to a fourth roof. Indeed, one may carry throughout the entire city through the courtyards and roofs, through the enclosed areas and roofs, or through the courtyards and the enclosed areas, or through [any combination] of these three types of areas, provided one does not bring this article into any of the houses [in the city].55 [The latter is forbidden] unless all [the inhabitants of] these different areas join together in a single eruv.

[Conversely,] if an article was located in a house at the beginning of the Sabbath, and it was later taken out to a courtyard,56 it may not be taken to another courtyard, to another roof, to the top of a wall, or to an enclosed area unless the inhabitants of all the areas through which the article passes join together in a single eruv.

When a cistern is located between two courtyards,57 it is forbidden to draw water from it on the Sabbath unless a partition ten handbreadths high has been erected58 so that everyone would be drawing water from his own property.

Where should the partition be erected? If the partition is above the water, it is necessary that at least one handbreadth of the partition descend into the water.59 If the partition was constructed within the water, it must project a handbreadth outside the water, so that one domain will be distinct from the other.

Similarly, if a beam four handbreadths wide60 has been placed over the mouth of the cistern, one may fill [his bucket] from this side of the beam, and the other may fill [his bucket] from the other side of the beam. Although the water is not divided below [the beam], it is considered as if one portion [of the cistern] were separated from the other. This is a leniency enacted by the Sages with regard to water.

When a well lies in the midst of a path61 between the walls of two courtyards, [the inhabitants of] both courtyards may draw water from it; there is no necessity for them to extend projections to the well.62 [This ruling applies] even though the well is more than four handbreadths from each of the walls. [The rationale is] that [the presence of] a colleague's [domain] does not cause a person to be forbidden to carry [when he is lifting an entity] through the air.63

[The following rules apply when the wall of] a small courtyard is broken down, opening [the courtyard] entirely to a large courtyard before the commencement of the Sabbath:64 The inhabitants of the large courtyard may establish an eruv for themselves and they are permitted to carry, for portions of their wall still remain [standing] on each side.65

The inhabitants of the small courtyard, by contrast, are forbidden to remove articles from their homes to the courtyard until they establish a single eruv together with the inhabitants of the larger courtyard. [The governing principle is that] the dwellings of the larger courtyard are considered to be [part of] the smaller courtyard, while the dwellings of the smaller courtyard are not considered to be [part of] the larger courtyard.66

When two courtyards have established a single eruv together through a shared opening or window, and that opening or window was closed on the Sabbath,67 [the inhabitants of] each of the courtyards may carry within [their own courtyard].68 Since [carrying] was permitted for a portion of the Sabbath, it is permitted for the entire Sabbath.

Similarly, if [the inhabitants of] two courtyards have each established a separate eruv and the wall between them fell on the Sabbath, [the inhabitants of each courtyard] are still permitted [to carry] within their original area.69 They may each take articles from their homes and carry them to the point where they could originally.

[The rationale is that] since [carrying] was permitted for a portion of the Sabbath, it is permitted for the entire Sabbath.70 Although the number of people [within the courtyard] was increased, an increase of people on the Sabbath itself does not cause carrying to be forbidden.

[In the instance mentioned in the first clause, if after the opening or window was closed on the Sabbath,]71 the window was opened inadvertently, or an entrance was made, or gentiles made [an opening] on their own volition, it is again permitted [to carry from one to the other].

Similarly, if two ships were tied to each other and an eruv was established between them, it becomes forbidden to carry from one to the other if the connection between them is severed.72 [This ruling applies] even if they are surrounded by a partition. If the connection was reestablished inadvertently, it is again permitted [to carry from one to the other].