Bava Basra chapter 5, mishnah 7, continues to deal with transactions of movable property - portable objects. As mentioned, there are two components to every transaction: the meeting of the minds, called gemiras daas, where the terms of the transaction and the price are established; followed by the second stage - the act of acquisition (maaseh kinyan), a specific action that effects the transfer.
Why money does not acquire movable property:
By Torah law, giving money effects the acquisition: once the buyer gives the money and the seller receives it, ownership is supposed to transfer. However, the Sages ruled that money does not acquire. Their concern was that the seller might not take responsibility for delivering the merchandise, and if a fire breaks out, he will not bother to protect the buyer's goods. Therefore, in order to obligate the seller with responsibility until delivery, the Sages ruled that ownership does not transfer until physical delivery takes place, and money alone is not sufficient.
Hagbahah and meshichah:
Acquisition by lifting (hagbahah): The basic and normal way a person acquires movable property - actually lifting the object. This action constitutes conclusive proof that the buyer has taken ownership of it.
Acquisition by pulling (meshichah): Sometimes lifting is not possible - a barrel of flour weighing a hundred kilograms is beyond a person's strength to lift. In such a situation, the acquisition is done by pulling: the buyer pulls and moves the barrel from its place instead of lifting it.
Acquisition by pulling is only effective in a place where the buyer has the right to be:
The buyer's private domain.
Shared space: Such as a seller and buyer who are partners and co-own a warehouse - pulling within the warehouse is effective.
An alleyway (simta): In the time of the Sages, based on how cities were planned, outside the main public domain and the main roads, there was a side path called a simta. The simta stands there specifically as ownerless property intended to serve people for making these types of transactions, and therefore pulling in a simta is effective for transferring ownership.
"Hamocher peiros lachaveiro, mashach velo madad - kanah" - One who sells produce to his fellow, if he pulled it but did not measure it, he has acquired it:
Reuven sells Shimon wheat, and the two agree on a price of ten shekels per kilogram. Before Reuven is a large container filled with wheat flour. Shimon pulls the container but does not measure it, and he does not know how many kilograms are inside it - meaning there is no clarity regarding the amount he must pay. Nevertheless, since the conditions were agreed upon, and once the buyer performed the pulling and transferred the container to a simta or to his private domain, the act of acquisition was done and the contents are acquired by him. Reuven can no longer back out, and it only remains to clarify the amount he needs to pay.
"Madad velo mashach - lo kanah" - If he measured it but did not pull it, he has not acquired it:
The terms were agreed upon - ten shekels per kilogram - and the merchandise was already measured: the seller measured and poured a hundred kilograms of flour into the buyer's vessel. But the buyer has not yet taken physical possession and did not pull the vessel, and therefore "he has not acquired it". The meaning of this is that he has the ability to back out. If at that moment he receives a message that the price of flour has dropped sharply and it can be purchased much cheaper elsewhere, Shimon is permitted to back out of the transaction.
As learned in tractate Bava Metzia, one who backs out after the terms have been agreed upon and before the transaction is completed, is subject to the Sages' curse known as "Mi Shepara": He who exacted payment from the people of the generation of the Flood and from the generation of the Dispersion, He will exact payment from that person who went back on his word. But apart from the curse, technically the buyer is operating within his legal rights and is allowed to back out; he will just be considered a bad person and receive a curse, since he is not keeping his word.
"Im hayah pike'ach - socher es mekoman":
Let us assume the buyer is concerned that the price of wheat will rise and wants to close the deal quickly, and he is facing a hundred containers of wheat that he cannot pull all at once. "Im hayah pike'ach" - if he is a smart person - "socher es mekoman" - he rents their place: The buyer temporarily rents, even for just one minute, the ground upon which the barrels he wishes to buy are resting, such as the seller's warehouse or the space in the warehouse beneath the barrels. This way, he is not required to carry a hundred barrels from the warehouse to the alleyway. Rather, he acquires what is resting on his rented space through an acquisition of courtyard (kinyan chatzer): A person's property, his courtyard, acquires on his behalf, provided that it is guarded and he is standing beside it.
The acquisition of renting the ground beneath the purchased merchandise is accomplished through money, a contract, or taking possession (chazakah), and therefore money is an effective means to execute it. The buyer gives a shekel to the seller - not to buy the wheat with it, but to rent the ground beneath it. Once the ground is rented to him, the courtyard, which is now his domain, acquires the merchandise on his behalf.
"Haloke'ach pishtan mechaveiro":
Flax is usually bundled in small quantities because it is delicate, and therefore it is not heavy, allowing each bundle to be lifted individually. Therefore, "harei zeh lo kanah ad sheyitaltelenu mimakom limakom" - the buyer does not gain halachic ownership until he actually lifts the bundles of flax and moves them from one place to another. What is required here is an acquisition of lifting (kinyan hagbahah).
"Im hayah mechubar lakarka vetalash kol shehu - kanah":
What is the halachah when the flax is still attached to the ground, and Shimon wishes to buy from Reuven flax that is standing in his field? The Mishnah states: "Im hayah mechubar lakarka vetalash kol shehu - kanah" - if it was attached to the ground and he plucked any amount, he has acquired it. Once Shimon plucks a single stalk from the ground, he acquires all the flax in the field.
Seemingly, this does not align at all with the rules that have been explained: plucking a single stalk of flax is not an act of acquisition for an entire field. Rather, behind the scenes, two stages are occurring here, and we are dealing with a situation where both the buyer and the seller understand both of them and agree to them:
Wages: The seller tells the buyer to do a little work for him to improve the field - to start the harvest by plucking the first stalk. This harvesting is worth a perutah, meaning that the seller now owes the buyer. Instead of paying him a shekel for his work, he rents the field containing the flax to him for a moment; meaning, the payment is given in the form of renting the property.
Kinyan agav (incidental acquisition): Flax that is fully ripe and needs nothing more besides harvesting is already considered movable property (metaltelin), even though it is attached to the ground, since it supposedly no longer needs it. Once the buyer becomes the renter of the property, he acquires incidentally along with the land - as if on its back - the movable property upon it as well. Additionally, one could say this is an acquisition of courtyard (kinyan chatzer), since the ground itself is now in his domain.
In summary: The payment for harvesting that single stalk is given by means of renting the field to the buyer for a moment, and upon receiving the field, and simultaneously with it, the buyer also acquires the flax growing in it. Thus, by plucking just one stalk, he acquires all the flax in the field.