Commentary for Kiddushin 124:14

The Talmud answers that conversion also cannot be done by the man himself, for he needs a court to convert and it is not clear that he will find three to serve for him in such a capacity.
Conversion is a legal matter (see Leviticus 24:22).
I should note that in earlier rabbinic literature it seems that conversion was a self-administered process. A person just decides to become Jewish, goes through the proper ritual and thereby becomes Jewish. Only later in the Talmudic period do we hear of the necessity for a court. I wrote an article about this—you can find it on academia.com if you are interested. And let me know what you think!

If R. Yohanan is correct, that if a person can do something, it is not as if that act is lacking even if he had not yet performed the act, then a man should be able to marry his slave woman, saying to her that she’ll be betrothed after he frees her. After all, he has the power to do so.
The Talmud rejects this (you probably won’t like the answer). Slaves are not considered to have the ability to consent. They are like animals. But after she is freed she is considered to have an independent mind. She would need to consent as a free woman in order to be betrothed.

It would seem that R. Yohanan should disagree with R. Oshaia. However, the Talmud resolves that R. Yohanan agrees because while a man can divorce his wife against her will (according to Talmudic law), he cannot marry her against her will. Therefore, this is not something that he can do.

If R. Yohanan agrees with R. Oshaia in the earlier case, then maybe we would have our answer to this other case, where a man tries to betroth a woman now and again after he divorces her, all within one act of betrothal. R. Oshaia did not know the answer to this, but it would seem that since he can’t marry her against her will after he divorces her, even if she consents now, the second kiddushin would not be valid.
The Talmud answers that maybe in this case her consent could carry over to the second kiddushin. Thus this question still remains.

One cannot separate terumah from attached produce for detached produce or vice versa. But if one adds in “when it is cut off” then the statement is valid, because he does have the power to cut the produce off.

R. Eliezer b. Ya’akov goes a step further and says that someone can do this even though the produce had not yet even grown to a third, which is when it becomes liable for terumah.

Fodder refers to the young plant that has grown less to one-third ripeness but is still useful for animal feed. While not liable for terumah, it still is usable. The soft plants have not even reached this state and therefore, Rabbah holds that one may not dedicate them to be terumah. R. Yosef disagrees.

R. Elazar explains the biblical etymology of the word “agam”—how do we know it refers to a soft plant. We should note that this word does not seem to be the same as the word “agam” which means lake.

Rabbah would say that a man can betroth the fetus only if the woman is visibly pregnant. R. Yosef would say that while she must be pregnant, the pregnancy need not even be discernible.

This is another version of Rabbah and R. Yosef’s dispute. Rabbah holds that to be separated as terumah, the fodder must be in a naturally watered field. Such fodder will definitely ripen because it receives its water naturally. But fodder in an artificially irrigated field might not ripen if no one waters it. Therefore, it cannot be separated. R. Yosef says it does not matter. In either case, the terumah may be separated even before the produce has ripened.

The mishnah about betrothing a fetus can only refer to a visibly pregnant woman, but now it is not connected to the dispute between Rabbah and R. Yosef.

The rabbis don’t like the simple reading of the verse, which seems to prohibit one from returning runaway slaves. While our sympathies will of course lie with the simple reading of the verse, rabbis did not oppose slavery (I’m not sure if anyone in the ancient world did). As such, it did not make sense to them that a slave could simply run away and thereby become free. Therefore, Rabbi limits the law to a particular type of slave. One that was bought under the condition that he be set free. But how does this happen? R. Nahman b. Yitzchak explains that the master wrote that when he buys the slave, the slave will be freed from this moment and on. Thus the slave can acquire himself even before the buyer buys him. This is considered a case of a person acquiring something not yet in the world.