Siman 372

Know, that when Solomon and his beit din decreed regarding eruvin, they only decreed regarding carrying from house to house, where usage is frequent and each person's dwelling is distinct from his fellow's. However, roofs, courtyards, and karpifot, where usage is not frequent but rather occasional—there are no distinctions of domains regarding vessels that rested within them and not in the house, and it is permitted to carry from the roof of Reuven to the roof of Shimon even without an eruv, and similarly from the roof of this one to the courtyard of that one or to the karpif of that one, and the like. This is what the sages taught in the Mishnah: (Chapter 9) "Whether roofs, courtyards, or karpifot—they are all a single domain for vessels that rested within them, but not for vessels that rested within the house." And such is the halacha, as we say in the Gemara (91a). And the general rule of the matter is, that anything that is a complete reshut hayachid, like those we have enumerated, and similarly a mavoi rendered permissible by a lechi and korah—they are permitted for carrying from one to the other, the vessels that rested within them. But vessels that rested within the house—the law of the house applies to them. That is to say, even if it stands in the courtyard—it is forbidden to carry it to the courtyard of his fellow or to the roof of his fellow, or to the karpif of his fellow or to the mavoi, because at the onset of Shabbat when it was in the house the prohibition took effect upon it, and since the prohibition took effect at the time of the onset of Shabbat—it takes effect for the entire Shabbat. And conversely, a vessel that was standing in the courtyard at the onset of Shabbat, and afterwards they brought it into the house, and then returned and brought it out to the courtyard—they are permitted to carry it to the courtyard, roof, and karpif of his fellow, and this is the general rule of the matter.

And in the Gemara there, there is a dispute, for there is one who holds: when do we say that all of these are one domain? When all the houses in the courtyard did not make an eruv, and it is forbidden to carry from the house to the courtyard, and then the vessels of the house are not commonly found in the courtyard. But when they made an eruv, such that the vessels of the house are commonly found in the courtyard, if we permit carrying from courtyard to courtyard, they will also carry the vessels of the house that are located in the courtyard—and therefore it is then entirely forbidden to carry from courtyard to courtyard, even vessels that were in them at the onset of Shabbat. And there is one who holds that there is no distinction between whether they made an eruv or did not make an eruv, and even if they made an eruv—they are permitted, and we do not decree regarding the vessels of the courtyard on account of the vessels of the house, as this would be like a decree upon a decree, and most of the poskim ruled accordingly, and so they ruled in the Tur and Shulchan Aruch.

This is the wording of the Rambam, chapter 3, law 18: "All the roofs of the city, even though this one is high and that one is low, along with all the courtyards and all the karpifot that were enclosed not for the purpose of dwelling and do not contain more than a beit satayim, along with the thickness of the walls between the courtyards, along with the alleys that have a lechi or a korah—all of them are one domain, and one may carry in all of them without an eruv vessels that were at rest within them, but not vessels that were at rest within the house, unless they made an eruv."

"How so? A vessel that rested within the courtyard, whether the residents of the courtyard made an eruv or did not make an eruv—it is permitted to bring it up from the courtyard to the roof or to the top of the wall, and from the roof to another roof adjacent to it, even if it was higher than it or lower than it, and from the other roof to a second courtyard, and from the second courtyard to a third roof of a third courtyard, and from the third roof to a mavoi, and from the mavoi to a fourth roof, until he moves it through the entire city via roofs and courtyards, or via roofs and karpifot, or via courtyards and karpifot, or via all three of them from this to that and from that to this. Provided that he does not bring this vessel into one of the houses, unless all the residents of these places made one eruv. And similarly, if the vessel rested in a house and he brought it out to the courtyard—he may not move it to another courtyard or to another roof or to the top of the wall or to a karpef, unless the residents of all the places through which they move this vessel made one eruv" thus far the words of the Rambam, of blessed memory. And see what I wrote in siman 388, section 4.

It is a simple matter that from all these places it is forbidden to carry to a karmelit. Therefore, it is forbidden to carry from a courtyard to a mavoi that does not have a lechi or a korah, for it is like a karmelit, and likewise from a roof or a karpef. And the karpef of which we said it is permitted to carry from it to a courtyard or a roof—this refers to a karpef of two beit se'ah that was not enclosed for dwelling, or more than two beit se'ah and was enclosed for dwelling. But more than two beit se'ah and not enclosed for dwelling—it is a karmelit, and it is forbidden to carry from it even to another karpef similar to it, except for two amot in this one and two amot in that one. And within it itself it is also forbidden to carry more than four amot, just as in a complete karmelit, like a sea or a valley. And all the more so is it forbidden to carry from it to a courtyard, a roof, or a karpef of two beit se'ah that was not enclosed for dwelling, or to more than two beit se'ah that was enclosed for dwelling, even two amot in this one and two amot in that one. (And in Rashi, Shabbat 130b, s.v. 'karpefot', he wrote: "And if it is more than two beit se'ah and was not enclosed for dwelling—it is called one domain regarding its fellow or regarding a courtyard, to carry two amot in this one and two amot in that one." Thus far his words. And certainly these three words 'or regarding a courtyard' are a printing error, for how could it be permitted from a karmelit to a courtyard? Rather, it is certainly an error, and examine this closely.)

There is one who says that vessels that rested in the house—it is forbidden to carry them from a courtyard to a karpef of less than two beit seah that was not enclosed for habitation, even if they belong to one person (Magen Avraham, subsection 1). And that which the Rambam wrote, which we brought in section 3, that roofs, courtyards, and karpifot are a single domain for vessels that rested within them, and not for vessels that rested within the house, unless they made an eruv, thus far his words—from which it is proven that if they made an eruv it is permitted—does not refer to karpifot, for an eruv is not effective for them, as even if they belong to one person it is forbidden (ibid.). For anything that was not enclosed for habitation is not included in an eruv, and it is a domain unto itself regarding vessels that rested within the house, even those of one person where an eruv is not required; and so wrote Rashi (23b, starting with "Datnan," see there) and Tosafot at the beginning of the chapter "Chalon" (starting with "Uvilvad"). And one should not ask according to this, that an eruv is not effective for karpifot that were not enclosed for habitation even less than two beit seah, and if so, when they make an eruv for an alleyway or the entire city, behold the courtyards are breached into the karpifot and it is a breach into a place forbidden to it. For it can be said that since for vessels that rested within them they are a single domain, such that it is permitted to carry from this to that—it is not called a forbidden place regarding that which it is forbidden to carry vessels that rested within the house.

In my humble opinion, it seems forced to explain the words of the Rambam as not referring to karpifot, for in truth, through an eruv, all karpifot smaller than two beit se'ah that were not enclosed for dwelling are nullified to the generality of the eruv. A proof for this is from that which we established above in siman 358, that a garden smaller than two beit se'ah which is a minority of the courtyard—it is permitted to carry from it to the house (the Magen Avraham himself wrote so there in subsection 14) because it is nullified regarding the courtyard, see there. And a garden is like a karpef that was not enclosed for dwelling, as is explained there, for seeds nullify the dwelling. If so, granted that a karpef, even if it is a minority of the courtyard, is not nullified regarding the courtyard like a garden—because it is a matter unto itself and is not similar to a garden which was a courtyard and became a garden—nevertheless, by means of an eruv it is nullified and enters into the category of the eruv. According to this, the Rambam refers also to karpifot. (See in the Ritva 23b, who wrote in the name of his teacher, the Ra'ah, of blessed memory, that according to Rabbi Shimon it is permitted to carry from a house to a karpef that was not enclosed for dwelling smaller than two beit se'ah when they belong to one person, and in this Rabbi Shimon is more lenient than the Rabbis even regarding vessels that rested in the house; and he brought one who disagrees on this, see there. However, in any case, by means of an eruv, one can certainly say that it is permitted, and examine this well.)

Two courtyard communities that wish to make an eruv together in order to permit carrying from the houses, if each courtyard made an eruv for itself—there is no need for a new eruv; rather, the residents of this courtyard bring their eruv into the house in the second courtyard where the eruv of the second courtyard is placed, and then they are all permitted to carry from the houses and they all become as one domain. And not everyone needs to bring their eruv, but rather one of the residents of the courtyard brings it on behalf of everyone, for he becomes like their agent. And it seems to me, that they must ask all the residents of the courtyards if they wish to make an eruv together, for even though regarding the eruv of each courtyard one does not need to ask, as one may acquire a benefit for a person in his absence, nevertheless with another courtyard perhaps it is not pleasing to them to increase the residents. And so it seems to me, that when each courtyard made an eruv for itself and now they combine their eruvim together as has been explained, it requires now a blessing for itself, and they do not fulfill their obligation with the previous blessing, for behold this is a different eruv. And they bless and say: "By means of this eruv, it shall be permitted for us to carry from the houses of the two courtyards from house to house, and from the houses to the courtyards, and from the courtyards to the houses."

And if each courtyard has not yet made an eruv for itself, they collect bread from all the houses of the two courtyards and place one eruv. And if one of the residents of the courtyards wishes—he may grant possession from his own on behalf of everyone, as with an eruv of a single courtyard. Nevertheless, there is a distinction between them, for he cannot go to the second courtyard and grant possession from his own on behalf of the two courtyards and make an eruv, for he has not yet been made an agent of his courtyard to make an eruv with the second courtyard. Rather, he first makes an eruv for his own courtyard by means of granting possession, and afterward for the second courtyard he is effectively their agent, since the eruv was made with their own. And so too if his courtyard does not require an eruv, such as if they all eat in one place, as I wrote in siman 370, one of them may go from the start to the second courtyard and make an eruv for everyone together from his own by means of granting possession. And this is the intention of our teacher, the Rema, in section 3, see there, provided that he tells them as I wrote.

Two courtyard areas cannot make an eruv together unless there is a doorway between them or a window of four by four, and provided that some part of the window is within ten tefachim of the ground. Then, if they wish, they may make an eruv together, and they are permitted to carry even through the holes of the walls or over the walls; and if they wish, each one may make an eruv for itself. And if the doorway is more than ten and does not have the form of a doorway, they are compelled to make one eruv for both of them, for if not, they will prohibit one another. And know, that the window must be four tefachim wide, even if it is very long, for anything that does not have four tefachim in its width is not a spacious place for use. And if the window is round, it must have a circumference of seventeen tefachim minus a fifth, and a tefach and four-fifths and a bit must be within the ten tefachim closest to the ground. (Gemara, beginning of "The Window," see there)

And this requirement of ours regarding a window, that part of it must be within ten—this is regarding a window between one courtyard and another. However, two houses that wish to perform eruv together by way of a window that is between this house and that house—they may perform eruv even if the window is entirely above ten, for a house is considered as if it is full, and it is not similar to a courtyard. And the reason is because the house is roofed and the courtyard is not roofed. Therefore, a window between two houses, even if it is above ten—if they wished, they may perform eruv together. And the same law applies to a hatchway in the roof between a house and an upper story; even if there is no ladder there to ascend from the house to the upper story—it is permitted to perform eruv together by way of the hatchway, when it is four by four wide. And one should not ask, when there is no ladder how do they ascend to the upper story, for it can be said that they ascend by a ladder to the upper story by way of the courtyard. And our teacher, the Rema, wrote in section 5: that if they made a grating in front of the window—it is nullified from the status of a window. Thus far his words. And a grating is a perforated iron gitter. And it seems to me, that this is when they placed it and attached it there permanently. But when they did not attach it—this does not nullify it from the status of a window.

It is a simple matter that the requirement for an eruv between house and house applies when they did not make an eruv in the courtyard; for if they made an eruv in the courtyard, all places are permitted and one may carry through any place he desires. And there is one who wishes to say that when they made a shituf in the alleyway, nevertheless, if there is no window or doorway between courtyard and courtyard, they are forbidden to carry through a hole between them, but only through the alleyway. And similarly regarding a courtyard and houses when they made an eruv in the courtyard, and there is no doorway or window between house and house—that it is forbidden to carry from house to house through a hole between them, but only through the courtyard. (Magen Avraham, subsection 3) And these are astonishing words that cannot be heard, for if so, we should also not carry from room to room by means of the eruv of the house through a hole between them; and how is it possible to say that in a place that is joined by an eruv they would say to him, "through here you are permitted to carry and through here you are forbidden"? Therefore, this law is not so. (And the Gaon Even HaEzer disagrees with him, see there, and the Tosefot Shabbat and the Pri Megadim cited this, and it appears they agree with his words. And the Magen Avraham, according to his reasoning, wrote in subsection 6 "through the courtyard," and the Tosefot Shabbat wondered at this, but according to his reasoning it is well, and examine it closely.)

If there was a wall ten tefachim high between the courtyards without a doorway or window, or if the ground of one was ten tefachim higher than its fellow, or if it was five tefachim higher than its fellow and he made a partition of five upon it to complete it to ten, and there is no doorway or window here—they cannot carry out an eruv both together; rather, each one carries out an eruv for itself, unless there is a mavoi and they carry out an eruv by way of the mavoi through shitufi mevaot. And also regarding this, it will be explained in siman 387 whether one relies on shituf in place of eruvei chatzerot, see there. And so too the opposite: if the courtyards are breached to one another in their entirety or by more than ten amot—they do not have the ability to carry out an eruv each one for itself, for they prohibit one another; rather, they carry out an eruv both as one. And all the more so if there is no partition ten tefachim high between them, for they only carry out an eruv together. And if there was a partition of ten between them with a doorway not more than ten amot, the choice is theirs—if they wish, they carry out one eruv; if they wish, they carry out two, each one for itself. And it is simple that if there was a tzurat hapetach between them, even with more than ten and even in its entirety— they can carry out an eruv each one for itself. And know, that less than ten and not in its entirety—nevertheless, there must remain either a post of four or two posts of any size according to the law of a courtyard.

A wall between two courtyards without a window or a doorway, where each must make an eruv for itself, or if there was a doorway or window between them and they desired to make an eruv each for itself, and there were fruits or other things that may be moved on Shabbat on top of the wall—the residents of the two courtyards may each bring them down into their own courtyard, and likewise may bring up fruits or an object from the courtyard onto it, for a wall and courtyards are one domain, as has been explained. Provided that they do not bring them down into the house, or from the house onto the wall, and also vessels that rested in the house are forbidden to be brought up from the courtyard onto the wall. However, in this there is a distinction regarding how much is the width of the wall from above, for if it is four tefachim wide, which has the measure of a karmelit—it is forbidden to bring down from it into the courtyard vessels that rested in the house. But if it is not four wide—it is a makom patur and is permitted, provided that they do not exchange, as I wrote in siman 346. And if the wall was ten high for one and for the second it is not ten high, because the ground of one is higher than its fellow and the wall is four wide, the courtyard in which it is not ten high—it is permitted to use it even with vessels that rested in the house when it made an eruv for itself, and the courtyard for which it is ten high—they are forbidden to use it even with vessels that rested in the courtyard. For since for its fellow this wall does not have the law of a roof, since for him it is not ten high it is for him like a courtyard, and it is permitted to carry upon it even vessels that rested in the house when it made an eruv for itself. And therefore if the second would use it with vessels that rested in the courtyard—he would give it the law of a roof, and automatically the first would be forbidden to use it with vessels that rested in the house, and it is not according to the law that he should forbid it to him. And if it is difficult: what did you see to give it all to the first and not even a part to the second? For such is the law, that any matter which for this one its use is with ease like this, where the height in it is not ten tefachim, and for this one it is with difficulty—we give it to this one whose use is with ease. (Gemara ibid.) But if the wall is not four wide, which is a makom patur—both are permitted to use it, even with vessels that rested in the house, as I wrote. (And this is the intent of the Magen Avraham, subsection 12)

A house standing between two courtyards, where each one made an eruv for itself and he made an eruv with both of them—he may carry everything to here and to there. And one should not say, how can a person dwell in two places? For this is not a question, as every person has the authority to dwell and to eat in several places, and all of them are considered dwellings for him. However, the residents of the courtyards cannot carry from courtyard to courtyard vessels that rested in the house by way of this person's house which is open to the two courtyards; only he is permitted to do so, because his dwelling is in both places and theirs is not.

Our Sages, of blessed memory, said (Avodah Zarah 59b) that a ladder has the status of a doorway. This means that when there is a wall between two courtyards and it has no doorway or window, if they place a ladder on this side and a ladder on that side, it is considered like a doorway, and they may join in an eruv together, for they may ascend this ladder and descend the ladder on the other side. And this specifically applies to a ladder that is four tefachim wide, meaning that the rungs must be four tefachim in width, and it must be a fixed ladder, which means it has no fewer than four rungs. But less than this is considered temporary and is not effective unless its rungs and the side posts are heavy, for then its weight establishes it as fixed. And one must place the ladder opposite the ladder on the other side, or within three tefachim of distance, so that one ascends from here and descends from there. But three, and certainly more, is not effective when the wall is less than four tefachim in width, for this is not a proper way of walking. But when the wall is four tefachim in width, even if the ladders are far from one another, one ascends the ladder and walks upon the wall until the ladder on the other side and descends to the courtyard, for a width of four tefachim is suitable for walking.

And the ladder must reach until the top of the wall, or less than three tefachim from its top. And it is not necessary to stand the ladder at an incline; rather, even upright it is considered like an opening, for this is like a platform, which also is not at an incline. (80a) And therefore, sometimes a ladder ten tefachim high is not necessary, such as when the wall is only ten tefachim—one stands next to it a ladder whose height is seven tefachim and a bit, and stands it next to the wall, and likewise from the second side. And the ladder is four wide as has been written, and the ladder is effective both for using the top of the wall, as this makes its use comfortable since he stands on the ladder and uses it, and for merging together, when he stands a ladder also from the second side, since there does not remain three tefachim until the top of the wall, and then regarding use on the wall both are equal, as is understood.

If the wall was made of earth and was higher than ten tefachim, and one removed a clod from the top of the wall to reduce it from ten in height, if there is a span of four tefachim in this—it is effective either to make it like a doorway to eruv together, if the removal is across the entire width of the wall from one side to the other, or if it is not from one side to the other, this person may use the entire wall, because for him its use is easy. And if there is not a span of four tefachim in the removal—it is not considered like a doorway to eruv together, and likewise it is not effective for using the entire wall, and he may only use it opposite the reduced area. And even though regarding a ladder that is not four wide, it is not effective even to use opposite it, this is because a ladder less than four has no permanence and he might take it from here. But regarding the removal of a clod—behold, opposite it at least its use is easy, and it is only for the entire wall that it is not effective, because it is not comfortable to stand upon it, but opposite it he stands on the ground and uses it.

If one built a platform next to the wall to diminish it from a height of ten, if it has four in length along the wall and also protrudes four tefachim, such that it is four by four—it is effective for using the entire wall. And even though for a ladder or a projection we do not require four by four, nonetheless for a platform we require it, for a platform is not comfortable to stand upon when it is not four by four; for with a ladder one holds the sides of the rungs, and similarly with a projection one steadies himself on the sides of the wall. But a platform, which is like a structure unto itself, if it is not four by four—it is nothing. And in any case, even with four by four, it is not considered like a doorway to make an eruv together until it reaches the top of the wall, or within less than three, and with a ladder it is also so. And only with a projection did we not require more than to diminish from ten, because it is from the body of the wall itself, and it is like a complete doorway. And if it is not four by four—it is not effective even to use opposite it, for the reason that I have written.

If one overturned a cup that is four by four and of any height, whether a little or a lot, and through it diminished the height from ten—it is permitted to use the area corresponding to the diminution, but not the entire wall. And it is inferior to a platform, because it has no permanence since he may take it from here, given that it is a vessel. (Magen Avraham, subsection 17) And some say that its law is like a platform, and one may use the entire wall. (Bach and Taz, subsection 7) And know, that with a cup it is not effective until he attaches it with clay, for if not so, it is nothing, as he would immediately take it. And he must attach it with a strong attachment, until he would be prevented from taking it from its place until he digs with a spade. But if only the clay is placed upon it—it is permitted to take it, and it is not a base for a forbidden thing regarding the clay which is muktzeh, for his intention is not that the cup should serve the clay such that it would be a base for it, but rather on the contrary, the clay serves the cup. Therefore, it is not applicable that the cup should be a base for the clay, as was written regarding a similar matter in siman 259, (Magen Avraham, subsection 18) and therefore this has no permanence until he attaches it strongly as has been written.

If one built a platform on top of a platform, if the lower one has four by four and it diminishes it from ten tefachim—it indeed diminishes, for he does not need the upper one at all. And even if the lower one does not have four by four but the upper one has four by four, and there are not three tefachim between the lower and the upper—it also diminishes, as we consider them as one. And even though this diminution is narrow from below, since its measure is completed from above and there are not three between them—it is a diminution. But when there are three tefachim between them—it is a diminution in the air, and it is not called a diminution. (Rashi, ibid. 77b) And this is effective only to use upon it, but it is not effective to become a doorway to join an eruv together, even if the second person also did so on the other side, until the platform reaches the top of the wall or within less than three. And this is according to the Tur and the Shulchan Aruch section 11. However, from the Rambam chapter 3, law 5, it is explained regarding a platform on top of a platform that if they wished they may join one eruv, see there, and perhaps his intention is when it reaches the top of the wall. (See Beit Yosef and see Maggid Mishneh there, law 13, who wrote that every diminution is until the top of the wall within less than three, and examine this carefully)

A projection protruding from the wall that is between two courtyards, which is like a board and has four by four, and one placed any ladder upon it, even if it does not have the measure of a ladder as has been explained—it is effective to permit him the use of the wall, when there are not ten tefachim from the projection to the top of the wall, for he stands on the ladder and ascends to the projection and uses the wall. And even though it is a temporary ladder, nevertheless, since it is adjacent to the projection, he will not remove it from there. But to join in an eruv together, even if the second also has such a thing—it is not effective, unless he supports it to the top of the wall or within less than three, (Magen Avraham subsection 19) and it is only effective for usage, as it is called "with ease" for this one, as has been explained. And this too is specifically that the bottom rung of the ladder should not be higher than three from the ground, so that it will be easy to ascend it, and likewise there should not be three between rung and rung. And even though regarding a fixed ladder we did not stipulate this condition, this is because it is a fixed ladder, and it is easy to ascend even with more than three, because the foot stands firmly. But here with a temporary ladder, when it is more than three, it is not easy to ascend it.

According to what we have explained, so it appears to me from the arrangement of the wording of the Tur and the Shulchan Aruch, that regarding a fixed ladder they did not write this condition, while regarding a ladder that is by the projection they explained this condition. However, according to what appears from the words of the Shas, it does not depend on this reason. And thus it is stated in the Gemara: (ibid.) "A ladder whose rungs are suspended... and there is not three between one and the other—it diminishes." And Rashi explained that a standard ladder is a ladder of steps, similar to those made among us fixed to ascend to upper stories, and they are like steps. And a ladder whose rungs are suspended is like our ladders, which are suspended one above the other and there is air between them, see there. And if so, the distinction is simple, for a ladder of steps which are wide, even though there is three between the bottom step and the ground and between step and step—it is easy to ascend, but this is not so with a standard ladder. And the Tur and the Shulchan Aruch who mentioned this detail regarding a ladder under the projection, I do not know their reason, and the Rambam indeed did not mention this regarding a ladder that is by the projection. However, this matter of "whose rungs are suspended"—they all omitted it, and the reason is hidden from me, and it requires further study.

And regarding a ladder that is by the ziz, it is necessary that the ladder be upon the ziz, which is to say that he should lean the top of the ladder against the ziz, for they are like a single thing. But to stand it adjacent to the ziz is not effective, for it is not a step for the ziz but rather widens it, and we require a step for the ziz. And behold, if the wall is not twenty tefachim high, one ziz is sufficient and he places it in the middle of the wall, so that there are not ten tefachim until the ground, and also until the top of the wall there are not ten tefachim. And he stands a ladder under the ziz as we have said, and ascends upon the ziz and uses the wall. And if the wall is twenty high, he needs two zizim, one within the lower ten and one within the upper ten. And he stands a ladder also upon the lower ziz, and ascends with it to the upper ziz and uses the wall. Therefore, he should be careful that the zizim are not exactly opposite one another, for it is impossible to stand a ladder in such a manner; rather, the upper ziz should be drawn away from the lower ziz along the length of the wall, and he shall stand a ladder upon it and lean it toward the side of the upper ziz. And even though we said regarding a fixed ladder that even when he stands it without an incline it constitutes a diminution—this is regarding a fixed ladder and by the wall. But a temporary ladder by the ziz, if it is not at a bit of an incline, he will not be able to ascend; therefore, when one ziz is drawn away from the second along the length of the wall, he can stand the ladder at a bit of an incline, as is understood. (So it appears in my humble opinion)

Regarding a ladder that is by the wall, if one did not have a ladder that was four tefachim wide, and he set up two ladders that together are four tefachim wide, and he acted so that it would be easy to ascend, meaning that he distanced one ladder slightly from the other and filled the space between them with straw, and his intention was that he would support himself with his hands on the ladders and with his feet he would ascend on the straw—it is not effective, for this is not an easy use to ascend on the straw. And it is not effective neither to permit him to use it, and certainly not to join in an eruv together, even if the second person does so from the other side, because the place of the foothold is in the middle of the ladder, and it is not good to ascend on straw. But the opposite is effective: that he sets the ladder in the middle and the straw on the sides, and he holds with his hands on the straw and his feet ascend on the ladder. Therefore, even if the ladder is not four wide, it is effective, whether to use the wall or to join in an eruv together if they do so from both sides, because this is a proper way of walking, provided that the ladder reaches the top of the wall as was written in section 17. (Magen Avraham, subsection 22)

If the ladder is not four wide, and he carved into the wall at the sides of the ladder from here and from there to complete it to four, such as where the wall is thick and protrudes from the side of the ladder, (Tosafot 78b, s.v. "hakak") it is sufficient for him to carve four at a height of ten. And even if the wall is very high, since the ladder reaches the top of the wall, and even though it is not four wide, nevertheless, since at a height of ten there is a width of four—it is like an opening. And if he did not set up a ladder at all, but rather carved into the wall like the rungs of a ladder to ascend by it—he must carve through the entire height of the wall, for it is not similar to a ladder which does not require four until the top of the wall, because on a ladder it is easy to ascend, but it is not so with carvings in the wall. Therefore, he requires four until its top, or less than three. (Gemara 78b) And the Rambam, chapter 3, law 11, turned this law to a completely different matter; see there.

Our teacher, the Beit Yosef, wrote in section 15: "If there was a tree at the side of the wall and he made it a ladder for the wall—if they desired, they may make one eruv. But if he made an asherah a ladder for the wall—they may not make one eruv, because it is forbidden to ascend it by the Torah, for it is forbidden for benefit. And the Rosh, of blessed memory, wrote the opposite: that a tree is not effective and an asherah is effective, provided that it is dry." Thus far his words. And the reason for the first opinion regarding a tree is that even though it is forbidden to use a tree, nevertheless, since this is only a shevut, and the time of the acquisition of the eruv is at twilight, and regarding anything that is a matter of shevut they did not decree at twilight; and even though here we require an opening for the entire Shabbat—nevertheless, the primary time is at twilight. Therefore, it is the opinion of the Rosh that it is certainly forbidden, for one requires a permitted opening for the entire day. And regarding the prohibition of an asherah, the Rosh holds that since it is a side prohibition and not from the prohibitions of Shabbat—we are not concerned with it. And if it is because it also contains a shevut, of using a tree, we are dealing with a case where it is dry. And even though above in siman 336 we forbid even in a dry one, nevertheless, the primary prohibition is in a moist one, and in a dry one they were stringent as a safeguard as is explained there, but the primary decree of the sages was only in a moist one. (See Magen Avraham subsection 26 who raised this difficulty, and according to what I wrote it works well, as is explained in Eruvin 100b, that they decreed regarding a dry one because it is not recognizable, see there.)

A trench between two courtyards that is ten deep and four wide, and runs along the entire separation between the courtyards, and there did not remain four tefachim together without a trench—it is a separation like a wall, and each one makes an eruv for itself and not both together. And even if they filled it with straw and stubble—it is not a sealing, as long as one did not explicitly nullify them so that they remain there permanently, and all the more so with fruit. But if it was full of dirt and pebbles, even if they did not fill it with the intent of nullification but it was filled on its own—ordinarily one nullifies them, unless one cleared them from there, and they must make an eruv specifically together. And nullification for one Shabbat—does not suffice to nullify a partition, for even though for other matters it suffices, it does not for the nullification of a partition. (ibid. subsection 27 in the name of Tosafot 84b s.v. 'Bor')

Our teacher, the Rema, wrote in section 16: "There are those who say that if one filled it with fruit without specification—they are nullified, for it is the way to make them a storehouse there." Thus far his words. That is to say, they disagree with the first opinion that requires permanent nullification, and nullification for this Shabbat is sufficient. And even though on this Shabbat as well one may take from there, as is written in siman 333, nevertheless, it is not the common way to use much until it is nullified from its state of being closed. (See Magen Avraham subsection 28 who raised this as a difficulty against the Rema, but the Eliyah Rabbah subsection 24 already answered as I have written. And that which the Gemara established on page 84a regarding a board, the same law applies to a storehouse; see there.)

If the trench was partially filled with earth or the like, which nullifies it permanently, if there is a span of four tefachim along the length of the trench—it is like an opening, and if they wish they may prepare an eruv together, and if they wish they may prepare two, and this is up to a span of ten amot. More than this—it is like a breach greater than ten, and they prepare one eruv and do not prepare two. (And this is the intention of the Ri brought by the Taz in subsection 9). And likewise, if one placed a board over the trench that is four tefachim wide, like a bridge from the edge of the trench from its edge to its edge—it is considered like an opening, and if they wish they may prepare an eruv together and if they wish they may prepare two, and likewise in this case up to ten—it is like an opening. More than this—it is like a breach, and they prepare one and not two. And if one placed the board along the length of the trench, and diminished its width until it does not have four in width, if he placed it over the entire length of the trench—the partition is nullified and they prepare an eruv together. And if not for the entire length—it is like an opening up to ten amot. Provided that it is over a span of four tefachim along the length of the trench, for if not so—it is nothing, and they prepare two. And if the trench for one courtyard is ten deep and for the second it is not ten deep, or if it is equal for both of them—in all this its law is like a wall as was explained in section 13 and in section 14, see there.

A stack of straw that is between two courtyards, if it is ten high—each one makes an eruv for himself, for it is a complete partition. And even though they will take it over the course of time, nevertheless, even a temporary partition is a partition, and the same law applies to a stack of grain or seeds. And if it was diminished on a weekday to less than ten tefachim—they must make an eruv together, but if it was diminished on Shabbat—we say "since it was permitted, it remains permitted," and if it was diminished up to ten amot—it is like an opening. And as long as it has not been diminished, it is forbidden for either of them to put from the straw into his basket on Shabbat to feed it to his animal, for we fear perhaps he will take so much until it is diminished from ten. And even though on Shabbat "since it was permitted, it remains permitted," nevertheless it is forbidden ab initio to do so. (Tashbetz, siman 555) And even to stand it there so that it may eat is forbidden, for there is also a concern of muktzeh in this. But he may stand before it from a distance, so that it does not stray to another place. And regarding the diminishing of the partition, there is no concern in its eating, for it will not eat so much until it is diminished from ten tefachim over a length of more than ten amot. And this law is similar to the law that was explained in siman 325 regarding a non-Jew who gathered grass, see there. (And with this one can settle the wonderment of the Taz, subsection 10, on the Bach, see there, though from the Beit Yosef it does not appear so, see there and examine carefully.)

And according to the Rosh, even on a weekday it is forbidden to place it into his basket, and likewise to stand an animal there by hand, for we fear that perhaps on Erev Shabbat it will be diminished to less than ten tefachim and he will not realize. However, regarding muktzeh—the Rosh does not hold of this, for here it is not muktzeh, as this is not like the dismantling of an ohel. (Magen Avraham, subsection 30) To what do these words apply? To a stack between two courtyards. But a stack between two houses, where each one makes an eruv for himself—it is permitted to place into his basket and to feed his animal from it by hand, for since there is a ceiling and a partition—it will be noticeable when it is diminished to less than ten tefachim over a span of more than ten amot. And it is not only necessary to say if the stack reaches the ceiling, that it will be noticeable when it is taken, but even if it does not reach the ceiling—it will also be noticeable when much is missing. (And what the Magen Avraham wrote in subsection 31, that one house is open to this courtyard and the second to another courtyard and the two courtyards did not make an eruv together, thus far his words, certainly one may say so, but this is not necessary, for one can say they are open to one courtyard, but that on this side there are two homeowners in two rooms who made an eruv together, and likewise on the second side. And when it is diminished to less than ten tefachim—they will forbid one another, and examine this closely.)