in a position of uncertainty, and Rabbi Yosei holds that a person does place himself in a position of uncertainty?

The Gemara raises a contradiction from the following mishna (Kiddushin 64b): In the case of one who has two groups of two daughters born to him from two women, e.g., he has two daughters from his first wife, and after his first wife died he remarried and had two daughters with his second wife, and he said: I betrothed my older daughter to someone, but I do not know if I meant the older of the older group of daughters; or if I meant the older daughter of the younger group; or if I meant the younger daughter of the older group, who is nevertheless older than the older daughter of the younger group, then all three of those daughters are prohibited to marry another man due to the uncertainty, as he failed to clarify which daughter was betrothed. This applies to all the daughters apart from the younger daughter of the younger group, who is certainly not betrothed. This is the statement of Rabbi Meir.

Rabbi Yosei says: They are all permitted to marry, apart from the older daughter of the older group. This demonstrates that according to Rabbi Meir, one must take into account any of the possible meanings of the imprecise expression: My older daughter, whereas Rabbi Yosei maintains that only the narrowest possible meaning of the phrase is taken into account. This contradicts the mishna here.

In response to this question, Rabbi Ḥanina bar Avdimi said that Rav said: The attribution of the opinions is reversed, i.e., the views stated in the mishna here must be reversed in order to reconcile them with the mishna in Kiddushin. And it is indeed taught in a baraita that this is the principle: With regard to any vow which specifies a fixed time, i.e., an event that occurs on a particular date, and one said that the vow applies until before that event, Rabbi Meir says the vow applies until the event ends, and Rabbi Yosei says that the vow is in effect only until the event arrives. This is another proof that the opinions in the mishna here must be reversed.

MISHNA: If one takes a vow that something is forbidden to him until the grain harvest, or until the grape harvest, or until the olive harvest, it is forbidden to him only until the arrival of that season. This is the principle: With regard to any occasion whose time is fixed, and one said: Until it arrives, it is forbidden to him until the specified occasion arrives. If he said: Until it will be, it is forbidden to him until the specified occasion ends. And with regard to any occasion whose time is not fixed, i.e., it does not fall on a precise date, whether he said: Until it will be, or: Until it arrives, it is forbidden to him only until the specified occasion arrives.

If he said: Until the summer [kayitz], or: Until it will be summer, the vow remains in effect until the people begin to bring fruit into their houses in baskets. If he said: Until the summer has passed, the vow remains in effect until the people set aside [yakpilu] the knives [hamaktzuot] with which the figs are cut after being harvested, and return them to their place of storage.

GEMARA: The Sage taught: The basket about which they spoke in the mishna is a basket of figs, and not a basket of grapes, which are gathered later than figs. It is taught in a baraita: One who vows that summer [kayitz] produce is forbidden to him is prohibited from partaking only of figs, as the fig harvest is called kayitz. Rabban Shimon ben Gamliel says: Grapes are included in the category of the summer produce, along with figs.

The Gemara asks: What is the reason of the first tanna? The Gemara answers: He holds that since figs are plucked [mikkatzetzan] by hand, while grapes are plucked not by hand but with tools, it is only figs that are considered summer [kayitz] produce. Conversely, Rabban Shimon ben Gamliel holds that grapes, too, when they are sufficiently ripe, are plucked by hand. Therefore, they can be considered summer produce as well.

§ The mishna states that if one said: Until the summer has passed, then the vow remains in effect until the people set aside the knives used to cut the figs. It was taught: This means until most people set aside their knives, even if there are still some individuals who have yet to do so.