Can A Minyan be Formed Across a Path?
If people are praying outside, some standing on one side of a path and some on the other, can they join together to form a minyan?
On one of my visits to an army base, I prayed together with the soldiers in front of one of the tents. A path leading to the tent and clearly marked on both sides by painted stones, separated between the people gathered for prayer. The question arose in my mind whether the path constitutes a separation, which would prevent the people standing on its opposite sides from joining together to complete a minyan of ten.
The Shulchan Arukh (Orach Chayyim 195:1) rules:
[When] two groups [of people] eat together in the same building, or in two buildings, and part of one group can see part of the other group, they may join together in a single zimmun; and if not, they may not join together… And this is where they came in with the intention of joining together. And some say that if a public domain separates between the two buildings, they can not join together under any circumstances.
The Taz (ad loc., no. 2) writes:
It seems that the reference here is not necessarily to a real public domain, which is sixteen cubits wide, but even a path belonging to an individual separates between them. As we learned at the beginning of Pe'a, brought in chapter Chezkat Ha-batim (Bava Batra 55b), that this [a private path] separates between domains with respect to pe'a and with respect to Shabbat. And if so, the same should apply here, for the same reason applies to it as to a public domain.
This ruling was stated with respect to zimmun, but the Peri Megadim (Eshel Avraham 55, 12) writes that it also applies to joining together for matters that require a minyan. The question that demands further examination regarding the application to our case is the requirement that the two groups “see each other” mentioned by the Shulchan Arukh. The Magen Avraham (55, no. 14) brings the Rashba (Responsa no. 96), that if they can see each other, they may join together for a minyan, even if the prayer leader is standing on a platform ten handbreadths high and four handbreadths wide, and the other nine are found down below. The Peri Chadash and Machatzit Ha-shekel also write that all the limitations mentioned by the Shulchan Arukh apply only to cases where they can not see each other, but when they can see each other, they can join together regardless. What, then, is the law regarding an intervening path; do we say that in this case as well that since they can see each other they can join together in a single minyan?
From the wording of the Shulchan Arukh in Orach Chayyim 195, who writes that if a public domain separates between two buildings, the people in them cannot join together in any circumstances, the implication is that this applies even if they can see other. It would seem reasonable to distinguish between joining for a minyan of ten and joining for zimmun, for regarding zimmun we need a stronger bond than for prayer. This can be learned from the Peri Chadash (55), who writes that with respect to zimmun, all must be able to see each other even if they are all in the same building, whereas with respect to prayer, he writes that people can join together as long as they are in one house, even if they cannot see each other.
However, such a distinction will not help in our case, for the Peri Megadim must be dealing with a case where they can see each other, for if we are dealing with a public domain that intervenes, we must be talking about people who are praying outside. And when they are not inside a building, what joins them together is the fact that they can see each other, for if they cannot see each other, what joins them together? And, furthermore, the Rashba's whole proof that people who can see each other can join together for a minyan is from zimmun. If so, just as in the case of zimmun, the ability of the people to see each other doesn't help when there is something that separates between them, the same should apply in the case of prayer.
The ruling cited above in the name of the Taz, that even a path belonging to an individual is considered a separation, should surely be followed in practice, for it is brought also by the Mishna Berura (195). Nevertheless, it seems to me that his position requires further examination, for the source of the Shulchan Arukh's ruling is Rabbeinu Yona (Berakhot 37b in Alfasi), who only mentions a public domain, without the comparison to pe'a. It is the Taz who adds that a path belonging to an individual, which is considered a separation with respect to pe'a and Shabbat, should also be considered a separation here, for the same reasoning applies.
It seems to me, however, that there is a fundamental difference between the realms. With regard to pe’a, the issue that needs to be determined is the definition of the place, whether it is considered one field or two. When the mishna (Pe’a 2:1) states, “The following cause a division with regard to pe'a,” it lists separations that split the field such that it is considered to be two fields rather than one. With regard to zimmun, at issue is not the definition of the place, but rather with the assessment as to whether the group of people is to be considered to be fixed in place for a shared meal. And indeed, while two houses are surely regarded as two places for all matters regarding definition of place, nevertheless, regarding zimmun, if groups of people in different houses can see each other, and they sat down with intent to joining together – they can combine. This being the case, why should the separation created by a path belonging to an individual make things worse than the separation cause by actual walls? Thus, when Rabbeinu Yona says that a public domain separates, he refers specifically to a public domain, for the passage of many people creates a separation not only to define the two sides as separate places, but also to define the people on each side as belonging to separate groups.
Proof to this may be brought from a fence that is ten handbreadths high, which is the classic case of a separation, about which we learn:
All [the above mentioned] separate in the case of vegetation, but in the case of trees nothing except a fence separates. If the branches intertwine, then [even a fence] does not divide and one pe'a is granted for the whole field. (Pe'a 2:3)
"Intertwined branches" means that the branches of the trees intertwine above the fence. The Yerushalmi (Pe’a 2:1) states regarding this:
This fence is connected and it is not connected. If you say it is connected, even intertwined branches would interrupt.
The Penei Moshe there explains that this means that the fence does not extend the entire length of the field, but rather intermittently, giving the overall appearance of separating the field into two. For regarding a separation that extends the entire length of the field, even intertwined branches would be considered an interruption. We see then that in the case of a complete fence, nothing can join the fields together. And yet in the case of two houses, there is a complete separation, and nevertheless they can join together with respect to zimmun if the two groups of people can see each other. Thus we are forced to the conclusion that the law regarding zimmun is different than that of pe'a.
There is another problematic issue that arises in this Taz. He cites the Gemara in Chezkat Ha-battim (Bava Batra 55b) that a path belonging to an individual separates between domains with respect to pe'a and Shabbat. But this is questionable, for with respect to Shabbat, the matter is the subject of a disagreement (Shabbat 80a). Rabba says that only a full-fledged public domain is considered to be a separation with regard to carrying, while Abbayei disagrees and says that even a karmelit (considered a public domain only rabbinically) separates. And the Halakha was decided in accordance with the opinion of Rabba that only a public domain is considered a separation (Rambam, Hilkhot Shabbat 18:24). We see then that a path belonging to an individual does not separate with respect to Shabbat. Why then should we learn zimmun from pe'a, and not from Shabbat?
Even according to the Taz, the question may be raised whether an area that is fenced in, like an army camp, can be divided by a path, for the laws regarding one who performs chazaka on part of the property of a proselyte who died leaving no heirs (whose property is transferred to the one who seizes it), whether he acquires all of his property, depend on the laws of separation regarding pe'a. [See the discussion there in Chezkat Ha-battim (55-56), and in Shulchan Arukh, Choshen Mishpat 275]. And see the Tur who writes regarding a field with fixed boundaries on all four sides:
If the property has fixed boundaries, e.g., where there is something that separates between them, whatever is within the boundaries is acquired with one strike of the spade.
The plain sense of his words implies that all those things that separate a field into two are discounted when the field has fixed boundaries. And while his demand is simply of a clearly evident boundary, not requiring a physical separation such as a fence, surely in our case, when the area is surrounded by an actual fence, a separation such as a path would be discounted. Yet, the Derisha emends the reading of the Tur and suggests that it should read, not: "when there is something that separates," bur rather: "when there is not something that separates," thereby limiting the Tur’s case to property with no legal separations within it. His reasons are not clear, and a proper analysis of his position is beyond the scope here. A certain proof can, however, be brought from the following mishna in Taharot (6:5):
If a man entered a valley in the rainy season and there was something impure in a certain field, and he stated: "I went into that place but I do not know whether I entered that field or not," Rabbi Eliezer rules that he is pure, but the Sages rule that he is impure.
See the commentary of the Rash there, who explains that the valley is not regarded as a single field, because the fields are set apart by fixed borders, or with things that separate fields with respect to pe'a.
See also mishna 7 there which states:
A valley in summer time is regarded a private domain in respect of the laws of Shabbat, but as a public domain in respect of those of impurity; and in the rainy season it is a private domain in both respects.
It would seem that the valley described in this mishna is the same type of valley as the one mentioned in the earlier mishna. The Gemara in Shabbat (6b-7a) cites this mishna and then brings a dispute among the Amoraim as to whether it speaks of a valley that has no partitions, so that it is a karmelit, or whether it has partitions, so that it is a private domain,. On the latter explanation, the valley mentioned in mishna 5, regarding which Rabbi Eliezer and the Sages disagree, is also surrounded by a fence Thus, this implies that even in a valley that is surrounded by a fence, those things that separate with respect to pe'a separate also with respect to impurity.
In conclusion, when people pray outdoors they should be careful that they are not separated by a road or a path, and if there are not ten people on one side of the path, then even if they can see each other they can not join together for a minyan, whether in the case of a field, or in the case of a closed camp.
As for the measurement of a path belonging to an individual, the Rambam (Hilkhot Mattenot Aniyyim 3:3) writes that if the path is not fixed in the rainy season, its measure is four cubits, and if it is fixed both in the hot season and in the rainy season, even a path that is less that four cubits wide separates. The Rash (Pe'a 2:1) writes that it is a very narrow path, the width being only so much as to allow him to lift up one foot and put down the other (based on Bava Batra 100a – see Rashbam there).
(Translated by David Strauss)
 The Gemara there addresses a case where one carries less two items, each of which is half the amount for which one would be liable between two domains. If the two items are carried to the same area they are considered together and the one who carries is liable. If they are carried to separate areas, they are considered separately and the one who carries is exempt. The dispute pertains to the type of separation necessary to consider the areas separate.
 Striking the ground with a spade is considered a display of ownership, a means of achieving chazaka.