Our Mishnah discusses the Din of partners who want to build a Mechitzah (partition) to divide their Chatzer - an area in front of the house, where people tend to conduct most of their affairs.

The Tana rules that, in such a case - they are both obligated to build the Mechitzah in the middle of their shared property (with each one supplying exactly half the materials and half the space).

They are obligated to follow local custom as regards which type of Mechitzah to build. If the Minhag is to build a Mechitzah of ...

... G'vil - a building-stone six Tefachim thick (as will be explained later), each one must supply a space of three Tefachim; of Gazis, which is five Tefachim thick, then each one provides a space of two and a half Tefachim.

... K'fisin - building bricks four Tefachim thick, each one must supply a space of two Tefachim; of Leveinin, which is a three Tefachim thick brick, then each one supplies a space of one and a half Tefachim.

Consequently, should the Mechitzah ultimately collapse - each takes half the bricks and half the space.

The Tana says that a shared ...

... vegetable-garden - has the same Din as a shared Chatzer, but not ...

... a wheat-field (as will be explained in the Sugya).

A partner who wants a Mechitzah in between his neighbor's wheat-field and his - must build it entirely in his own domain. To prove that the Mechitzah is exclusively his, he builds a Chazis (a projection along the length of the top) jutting out in the direction of his partner's field).

If they both want the partition Mechitzah - then they must build two Chazi'os, one jutting out in each direction.

The Halachic difference between the last two cases, should the Mechitzah subsequently fall down are - that in the first case, the partner who built the Mechitzah takes both the space on which the Mechitzah stood and the bricks; whereas in the second case, each partner takes half of each.

The advantage of a dividing Mechitzah between Reuven's wheat-field and Shimon's vineyard is - that now Reuven may plant wheat right up to the Mechitzah, instead of having to leave a space of four Amos (for Avodas ha'Kerem).

If such a Mechitzah collapsed, and after Shimon had rebuilt it, it fell down again, and although they asked him to repair it, he despaired from doing so - the Beraisa rules that the moment the wheat increased by one two-hundredth, it renders the mixture forbidden because of Kil'ayim.

We prove from the fact that the Beraisa uses the term 'Mechitzas ha'Kerem" (which is a stone Mechitzah) - that 'Mechitzah' in our Mishnah means a stone-Mechitzah, too.

Having proved that 'Mechitzah' means a stone-Mechitzah, we extrapolate from the Mishnah's use of the word 'she'Ratzu' ('ha'Shutfin she'Ratzu La'asos Mechitzah') - that if they do not both agree to build a Mechitzah, one cannot force the other to do so.

This teaches us the principle that 'Hezek Re'iyah Lav Sh'meih Hezek' (visual damage [in the form of being watched by one's neighbor as one works in the Chatzer] is not considered damage). Otherwise, the Mechitzah would be obligatory.

Querying our previous conclusions, we suggest that perhaps 'Mechitzah' means a division, (as in the Pasuk in Matos "Vat'hi Mechtzas ha'Eidah"), in which case the Tana would be coming to teach us - that the moment they agree to partition the Chatzer, they are both obligated to build a Mechitzah, because 'Hezek Re'iyah Sh'meih Hezek'.

We refute this suggestion however, on the grounds - that the Tana should then rather have said 'ha'Shutfin she'Ratzu Lachatzos'.

We try to counter this by pointing out, that even if 'Mechitzah' means a Mechitzah, the Tana should have said 'Bonin Oso' (rather than 'Bonin es ha'Kosel'). We refute this Kashya however, on the grounds - that seeing as Mechitzah also incorporates a Mesipas (a thin Mechitzah), had the Tana merely said 'Oso', it would have sufficed to build a Mesipas, and not necessarily a stone Mechitzah.

Even though the partners agreed to partition the Chatzer, the Mishnah sees fit to state that they build it in the middle - because he is speaking even in a case where one of the partners has convinced the other one to build. And he is coming to teach us that, having agreed to do so, he cannot argue that he only agreed to partition the Chatzer with a Mesipas, but not a Mechitzah (and that if Reuven now wants a Mechitzah, then he must move back into his own domain and build it).

We can extrapolate from the continuation of the Mishnah 've'Chein be'Ginah' (see Tosfos) - that 'Hezek Re'iyah Sh'meih Hezek'.

We reconcile this with the Reisha, which, as we just explains, holds 'Hezek Re'iyah La'av Sh'meih Hezek' - based on the fact that the Hezek Re'iyah is far more potent in a vegetable garden than it is in a Chatzer.

Despite the fact that a Mechitzah in a vegetable-garden is due to Hezek Re'iyah, whereas in a Chatzer it is not, as we just explained, the Tana says 've'Chein be'Ginah' - with regard to the type of Mechitzah that one is obligated to build ('Gvil or Gazis ... ), and not to the reason for the obligation.

The reason for the distinction is based on a statement by Rebbi Aba Amar Rav Huna Amar Rav, who said - that it is prohibited to stand in one's fellow-Jew's vegetable-garden when the vegetables are fully-grown (see Tosfos 'Ginah Sha'ani').

We reconcile the Mishnah later 'Kosel Chatzer she'Nafal, Kofin oso Li'venos ad Arba Amos' with the ruling 'Hezek Re'iyah Lo Sh'meih Hezek' - by confining it to a Mechitzah that was originally built jointly, and then collapsed (as the Tana specifically says).

The answer seems obvious. When we asked the Kashya however, we understood that the Tana presented the case of a Mechitzah that fell down, rather than the original one (even though the Din is the same in both cases) - because of the Seifa, which absolves them from building it higher than four Amos, even though it was higher before it collapsed.

The Mishnah later obligates each member of the Chatzer to pay towards building a small hut and a little door at the side of the main gate (as will be explained there). The purpose of the side door and the hut - is to prevent people from peeping into the Chatzer and to hire a guard to stop them from doing so, respectively.

We reconcile this with our Mishnah, which holds 'Hezek Re'iyah La'av Sh'meih Hezek' - by differentiating between the Hezek Re'iyah of an individual and that of the public.

The Mishnah later implies that if a Chatzer is large enough for each partner to receive four Amos, then one partner can force the other to partition it. If, as we currently hold, 'Hezek Re'iyah La'av Sh'meih Hezek', it will only need to be partitioned - with a Mesipas.

The Mishnah later requires a member of the Chatzer who decides to build a Mechitzah in his section of the Chatzer to ensure that it is at least four Amos higher and four Amos lower than all the windows, and four Amos away from them. It needs to be ...

... four Amos higher - to prevent the owner of the Mechitzah from leaning on his Mechitzah and looking into his neighbor's window.

... four Amos lower - to prevent him from standing on the Mechitzah and looking in.

... four Amos away - to prevent him from depriving his neighbor of light.

We reconcile this with our Mishnah which holds 'Hezek Re'iyah La'av Sh'meih Hezek' - by differentiating between the Hezek Re'iyah of a Chatzer and that of a house, where one requires more privacy.

In spite of the fact that 'Hezek Re'iyah La'av Sh'meih Hezek', Rav Nachman Amar Shmuel requires Reuven, the owner of a roof that adjoins Shimon's Chatzer, to build a parapet four Amos high at the edge of his roof - because it is more difficult for Shimon, who uses his Chatzer at regular hours, to anticipate when Reuven intends to use his roof, which one tends to use at more erratic times.