פירוש על קידושין 44:6

Money and deed acquire Canaanite slaves, just as they acquire Hebrew slaves. In addition, Canaanite slaves can be acquired through “possession”, which could also alternatively be translated as “presumption of ownership.” We learned the rules of possession in the third chapter of Bava Batra. Practically this would mean that a slave, who treated a certain person as if that person were his owner, would become the property of that person.

Both Rabbi Meir and the Sages agree that a slave acquires his freedom either through a manumission document or through his freedom being purchased with money. However, they disagree over whether or not the slave may purchase himself back. According to Rabbi Meir a Canaanite slave can never own property. Any property which he would acquire would automatically become the property of his owner, since the owner owns the slave. Therefore, only other people may purchase the slave’s freedom. When it comes to a document, the document must be received by the slave himself.
The Sages disagree on both counts. They hold that a slave may, under certain circumstances, own his own property. This is possible if other people give the slave money with the condition that the owner not take possession of that money. According to the Sages either he or others may purchase his freedom. Similarly, they disagree about the document. The master can write out a manumission document, give it to another person beside the slave and thereby free the slave. Note that the Sages could have stated that “a slave is acquired by documents or money through his own agency or the agency of others.” This would have been a clearer and slightly briefer statement of the sages’ intent. Instead, the mishnah phrases their statement as the opposite of Rabbi Meir’s statement in order to retain the parallelism.