The subject of קניין סודר ("Kinyan" by handkerchief) acquisition by means of exchange of a handkerchief needs some clarity.
It comes up in the Tosphot HaR''id in Kidushin page 3.
But just for background information, I want to explain what the issue is.
It all starts from the Mishna there that, "A woman is acquired by money, document, or sex." The Gemara says that is meant to exclude barter. That also excludes exchange of a handkerchief.
["Why would we think that a woman is acquired by barter? Because we learn קיחה קיחה משדה עפרון acquisition is said by the field of Ephron. And the same word acquisition is used in discussing when one marries a woman. כי יקח איש אישה. From where we learn a man can acquire a woman by money just like a field is bought with money. (That is why you see nowadays people marry by means of a ring.) So you might think barter also would work since a field can also be bought by barter. But the Gemara says we would not learn that way because barter can be less than a penny and a woman would not want to be acquired for less than a penny."]
The idea is that when one marries a woman two kinds of acquisition take place; (a) acquisition of marriage. The idea is that a person can be obligated by means of a "Kinyan" [acquisition]. For example to sign a contract to produce an F-35 in a certain amount of time. This creates an obligation on a person to do the work. [It does not have to be a document. It can be by any kind of kinyan (acquisition) that an obligation is made. Nowadays we depend a lot on documents, but in fact acquisitions can be made by lots of things. [Pulling, pushing, lifting up. For example, if one buys a piano. How do you acquire it? Not by lifting surely. Not by money either. If you paid money and then want out of the deal you get the money back. So you would have to move the piano. And then the deal is finished.]] Another thing that happens when you marry a woman-(b) an acquisition of monetary obligations.
So the idea of the mishna is if one marries a woman by any one of those three ways in front of two witnesses, then these obligations are חל ("hal") that settle on you and her. That is: the acquisition takes place.
[The ring used nowadays is for שווה כסף (something worth money). That is learned from a Jewish slave that can be redeemed by money (if he is owned by another Jew). However let's say a Jew is sold or sells himself to a gentile in order to pay for some obligation. Then how can he be let go if the owner wants to let him go? One way is if someone gives to the owner some money. [I do not think paper money works here.] Another way is a document. But not by means of something worth money. So we see there are times that something worth money is not counted as money. -even if the owner wants to accept the object worth money instead of money, that does not help. It has to be money. But in terms of marriage it is thought to be considered as money.
[This actually brings up a question asked by Rav Shach and Rav Haim of Brisk. That is, that acquiring a woman by something worth money is learned from a Jewish slave. So since it does not work in all cases with a Jewish slave, why should it work at all with a woman? It is a half a gezera shava. [That is sometimes when the same word is used to two places the laws of one place are applied to the other place except when you can only learn half. Then it does not apply at all.]
It comes up in the Tosphot HaR''id in Kidushin page 3.
But just for background information, I want to explain what the issue is.
It all starts from the Mishna there that, "A woman is acquired by money, document, or sex." The Gemara says that is meant to exclude barter. That also excludes exchange of a handkerchief.
["Why would we think that a woman is acquired by barter? Because we learn קיחה קיחה משדה עפרון acquisition is said by the field of Ephron. And the same word acquisition is used in discussing when one marries a woman. כי יקח איש אישה. From where we learn a man can acquire a woman by money just like a field is bought with money. (That is why you see nowadays people marry by means of a ring.) So you might think barter also would work since a field can also be bought by barter. But the Gemara says we would not learn that way because barter can be less than a penny and a woman would not want to be acquired for less than a penny."]
The idea is that when one marries a woman two kinds of acquisition take place; (a) acquisition of marriage. The idea is that a person can be obligated by means of a "Kinyan" [acquisition]. For example to sign a contract to produce an F-35 in a certain amount of time. This creates an obligation on a person to do the work. [It does not have to be a document. It can be by any kind of kinyan (acquisition) that an obligation is made. Nowadays we depend a lot on documents, but in fact acquisitions can be made by lots of things. [Pulling, pushing, lifting up. For example, if one buys a piano. How do you acquire it? Not by lifting surely. Not by money either. If you paid money and then want out of the deal you get the money back. So you would have to move the piano. And then the deal is finished.]] Another thing that happens when you marry a woman-(b) an acquisition of monetary obligations.
So the idea of the mishna is if one marries a woman by any one of those three ways in front of two witnesses, then these obligations are חל ("hal") that settle on you and her. That is: the acquisition takes place.
[The ring used nowadays is for שווה כסף (something worth money). That is learned from a Jewish slave that can be redeemed by money (if he is owned by another Jew). However let's say a Jew is sold or sells himself to a gentile in order to pay for some obligation. Then how can he be let go if the owner wants to let him go? One way is if someone gives to the owner some money. [I do not think paper money works here.] Another way is a document. But not by means of something worth money. So we see there are times that something worth money is not counted as money. -even if the owner wants to accept the object worth money instead of money, that does not help. It has to be money. But in terms of marriage it is thought to be considered as money.
[This actually brings up a question asked by Rav Shach and Rav Haim of Brisk. That is, that acquiring a woman by something worth money is learned from a Jewish slave. So since it does not work in all cases with a Jewish slave, why should it work at all with a woman? It is a half a gezera shava. [That is sometimes when the same word is used to two places the laws of one place are applied to the other place except when you can only learn half. Then it does not apply at all.]
