Bava Batra 76A

ובשטר.

and by means of a bill of sale.

אותיות מאן דכר שמייהו? חסורי מחסרא, והכי קתני: ספינה נקנית במשיכה, ואותיות במסירה. רבי נתן אומר: ספינה ואותיות נקנות במשיכה ובשטר.

The Talmud clarifies the baraita: Letters in promissory notes, who mentioned anything about them? Why would R' Natan speak about promissory notes, which are not discussed by the first tanna? The Talmud answers: The baraita is incomplete, and this is what it is teaching: A ship is acquired by pulling, and letters, i.e., the content of a promissory note, are acquired by merely transferring the document, not through pulling. R' Natan says: A ship and letters are acquired by pulling and also by means of a bill of sale.

שטר לספינה למה לי? מטלטלי היא! אלא לאו הכי קתני: ספינה נקנית במשיכה, ואותיות במסירה. רבי נתן אומר: ספינה במשיכה, ואותיות בשטר?

The Talmud asks: Why do I need a bill of sale for a ship? A ship is movable property, which is acquired not by means of giving a bill of sale, but through other acts of acquisition. Rather, is it not correct to say that this is what the baraita is teaching: A ship is acquired by pulling, and letters of credit by passing. R' Natan says: A ship is acquired by pulling, and letters, i.e. the contents of a promissory note, are acquired either through pulling or by means of a bill of sale.

ספינה במשיכה ⁠– היינו תנא קמא! אלא דרב ושמואל איכא בינייהו? לא; דכולי עלמא ⁠– אי כרב, אי כשמואל, ובספינה כולי עלמא לא פליגי;

The Talmud asks: If R' Natan holds that a ship is acquired by pulling, his opinion is apparently identical to the opinion of the first tanna. Rather, the practical difference between the two opinions is the dispute of Rav and Shmuel. According to the opinion of one tanna the buyer must move the entire ship out of its current location, while the other tanna maintains that one must move the ship only a minimal amount. The Talmud rejects this suggestion: No, everyone, R' Natan and the first tanna, holds either in accordance with the opinion of Rav, or in accordance with the opinion of Shmuel. And with regard to a ship, everyone agrees that it is acquired through pulling.