Kiddushin, Chapter 1, Mishnah 3. This mishnah deals with two topics: the ways in which a Canaanite slave, a non-Jewish slave, is acquired, and the ways in which he leaves the system and becomes a free man.
The ways a Canaanite slave is acquired:
The wording of the mishnah: "Eved kena'ani nikneh b'chesef u'vishtar u'vachazakah" - a Canaanite slave is acquired with money, with a document, and through chazakah.
"B'chesef" - with money. If the slave belonged to another master, paying money to that master acquires him.
"Bishtar" - with a document. Writing a bill of sale to the previous master.
"Bachazakah" - through an act demonstrating ownership. That is, making use of the slave in a way that shows he belongs to the buyer, such as having him dress his master or wash him - acts that a slave performs for his master, through which it becomes clear who the new owner is.
The Gemara adds two further methods of acquisition:
Chalifin (exchange) - the buyer gives the previous owner some other object, the owner acquires that object, and in return he hands over the slave.
Meshichah (pulling) - physically drawing the slave toward the buyer.
Why did the mishnah not list these methods? Because it sought to list specifically those methods of acquisition that apply to land and not to movable property, whereas chalifin and meshichah are performed with movable property.
The slave going free:
The mishnah continues: "V'koneh es atzmo b'chesef al yedei acherim, u'vishtar al yedei atzmo - divrei Rabbi Meir" - and he acquires himself with money through others, and with a document through himself; these are the words of Rabbi Meir. The money is given to the master by other people, while the document of release is handed over from the master into the hands of the slave himself.
The basis of Rabbi Meir's position:
With money - through others: the hand of the slave is like the hand of his master, and there is no way to transfer money to a slave without its automatically entering his master's possession. Therefore the payment for the release can reach the master only from a third party, who hands it to the master directly.
With a document - through himself: a slave going free is a liability and not a benefit, since it is not to his advantage to go free - as a slave he is cared for, and so on. And one cannot impose a liability on a person through a third party without his consent, and therefore others cannot receive the document of release on his behalf; rather, he must receive it himself. And even though his hand is like his master's hand, Rabbi Meir holds that his document of release and his hand come simultaneously: at the moment the document is handed over he becomes a free man, and it turns out that he took it into his own possession and not into his master's possession.
The opinion of the Sages:
The Sages say "b'chesef al yedei atzmo, u'vishtar al yedei acherim" - with money through himself, and with a document through others. The money can come from him himself, as long as it was given to the slave on condition that his master have no ownership in it whatsoever; once he becomes the owner of that money, he can give it to his master and thereby acquire himself. Of course others can give the money as well, but according to the Sages it can also be done by the slave himself. As for the document, others can receive it on his behalf, because according to the Sages going free is a benefit and an advantage for the slave, and therefore a third party can acquire it on his behalf.
Even so, the mishnah emphasizes that even according to the Sages, the slave takes the money and gives it to his master only when the funds were given to him by a third party on condition that the master have no control over them.
The Gemara's question:
According to the Sages, both the money and the document can be done either through himself or through others. If so, why did the mishnah state "with money through himself and with a document through others," rather than including both together and saying that money and a document are done through himself or through others?
The Gemara answers that the latter clause - "and with a document through others" - is not the opinion of the Sages but the opinion of a third Tanna, Rabbi Shimon ben Elazar, who holds that both of them, money and document, can be done only through a third party and not by the slave himself.
Rabbi Shimon ben Elazar holds that going free is to the slave's advantage, and therefore the document can be handled by a third party. But he does not accept the principle that at the moment he receives the document his hand is no longer like his master's hand, and for that reason it can happen only through a third party. And so too with the money: in his view there is no possibility of the slave holding money himself, and therefore the money too must be delivered by a third party.
It emerges that the statement "with money through himself" is the opinion of the Sages, while the statement "and with a document through others" is the opinion of Rabbi Shimon ben Elazar.
In summary: in this mishnah we learned that a Canaanite slave is acquired with money, with a document, and through chazakah - the methods of acquisition that apply to land - whereas chalifin and meshichah, which are methods of acquiring movable property, were not listed in the mishnah even though he is acquired through them as well. Regarding his going free, the Tannaim disagree: according to Rabbi Meir the money is given through others (since the hand of the slave is like the hand of his master) and the document through himself (since release is a liability, and his document of release and his hand come simultaneously); according to the Sages the money may be given even by himself, provided it was given to him by others on condition that his master have no ownership in it, and the document may be received even through others, since release is a benefit; and according to Rabbi Shimon ben Elazar, even though release is a benefit, both the money and the document can be done only through others.