Question

With the approach of summer, Yoni wishes to install an
air conditioning system in his apartment. The most suitable place for
hanging the outside unit is above the porch of his neighbour, Benny. Benny
initially agrees to the installation of the unit above his porch, since he
has plenty of room for a succah elsewhere. Since Yoni is making a major
investment, he wants to be sure Benny doesn’t change his mind. He therefore
draws up a document which reads as follows: Benny agrees to sell the
airspace above his porch to Yoni solely for the purpose of installing an air
conditioning unit. Yoni will pay Benny $100 for the privilege. The parties
signed the document and made a kinyan
(an act of acquisition) to seal the deal. When Yoni came to pay the agreed
fee three days later, Benny tells him that he has changed his mind. Yoni
argues that Benny is unable to back out of his contractual obligation. Is
his argument valid?

Answer

The Talmud Yerushalmi (Bovo Basro 3:1)
informs us that if a person sold the airspace above his ruin (or any other
property), the sale is invalid. The Pnei Moshe explains that the
buyer wished to purchase the right to build a ledge above his neighbour’s
land. However, the act of acquisition is ineffective since there is no item
of substance on which it can take hold. The Rosh (Bovo Basro
4:17) explains that in the same way as it is impossible for a person to
transfer ownership of an item which has not yet come into existence (dovor
shelo bo l’olam) it is also impossible to transfer airspace. If the wall
of Reuven’s house overlooked Shimon’s courtyard, Shimon is unable to sell
him the airspace above the courtyard for the purpose of erecting a shelf (in
modern terms, an air conditioning unit or window bars) since air can not be
sold. How can he transfer these rights? Let Shimon sell Reuven part of his
courtyard for its airspace. This will be effective, argues the Rosh, in
the same way as one can sell a bare tree for its future crop. The
problem of selling an item which has not yet come into existence is overcome
by attaching it to an item which does already exist. Similarly, the problem
of selling an item which has no substance (dovor she’ain bo mamash)
can be overcome by attaching it to a substantial item. This law is
quoted by the Shulchan Oruch (Choshen Mishpot 212:2).

How strong is the parallel between transferring
non-existing items and those which are non-substantial? Although one can not
transfer an item which does not exist, one can enter into a binding
obligation to transfer it at a later date. Would the same idea apply to a
non-substantial item? Perhaps a signed agreement to transfer such an article
at a later date would be valid, even though one is unable to transfer
ownership at the present time. On the other hand one could differentiate
between the two cases. Even though a particular item is not yet in existence
at the moment, it will later come into being. Since it will later become an
item of substance, we can argue that the obligation to make a transfer does
take effect. However, airspace has no substance and never will. Since the
obligation does not fall on an item of substance, it is still invalid. The
Emek HaMishpot (1:10) quotes the opinions of the Mahari ben Lev
(1:61), the Divrei Chayim (Choshen Mishpot 31) and the Oruch
HaShulchan (Choshen Mishpot 212:2 and 60:11) that here the comparison to
a non-existent item is not valid. The Oruch Hashulchan argues that an
obligation to transfer a non-existent item comes into effect when the item
comes into being. An item which has no substance now will always remain
non-substantial. We can therefore conclude that Benny can not be forced to
allow Yoni to install his air conditioner over his porch.