The Mishnah taught that one can acquire a Jewish slave using a document.

R. Abahu: The slave must write in the document, "I am sold to you for such and such amount of money''. However, he may not write that he is giving himself as a gift, as he might retract, which would retroactively annul the sale.

Question: If so, he could also retract even if he wrote an amount (by the slave giving back the money)?! (Note: This entry and the next one follow the explanation of the Pnei Moshe.)

Answer: If a year of famine comes, the master might wish to retract on the acquisition - therefore, a gift document is not valid since the slave will not rely on it and will not allow himself to be acquired because of concern that the master will free him due to lack of food. However, if it is a sale document the master will not readily free him since he will lose the money he gave.

The text of acquisition into slavery through a document is - "I, ploni, sold my daughter to ploni''.

The text of acquisition into marriage of a document is - "I, ploni, gave my daughter in marriage to ploni''.

Question (R. Chagai to R. Yosi): What if he switched it around and said, "I, ploni, a bought the daughter of ploni'' or "I, ploni, betrothed the daughter of ploni''?

R. Yosi replied: That would be fine, but if he referred to a sale using a wording of Kidushin or vice versa, he has not done anything at all.