אימא סיפא אמרו לו לרבי אליעזר אם מטבילין כלי טמא ליטהר יטבילו כלי לכשיטמא ליטהר שמע מינה חיילין

The Gemara rejects this conclusion and refers back to the baraita. Say the latter clause of that baraita: They said to Rabbi Eliezer: If one immerses an impure vessel to purify it, shall one immerse a vessel in advance so that when it will become impure it will then be purified? Learn from this clause of the baraita that according to Rabbi Eliezer, vows nullified preemptively take effect momentarily and are then immediately nullified. The Rabbis’ objection is that according to Rabbi Eliezer, prior immersion should purify an item that momentarily became impure.

אמרי רבנן לא קיימי להון בטעמיה דרבי אליעזר והכי קאמרי ליה מאי סבירא לך אי סבירא לך דחיילין ובטלין תהוי כלי תיובתך אי לא סבירא לך דחיילין תהוי מקוה תיובתך

The Gemara rejects this conclusion: One could say that the Rabbis could not determine the reasoning of Rabbi Eliezer, and this is what they said to him: What do you hold? If you hold that preemptively nullified vows take effect momentarily and are then nullified, then the example of a vessel will be your refutation, i. e., will serve to refute your opinion. If you do not hold that they take effect, but rather that they do not take effect at all, then the example of a ritual bath will be your refutation.

תא שמע אמר להם רבי אליעזר ומה זרעים טמאים כיון שזרען בקרקע טהורין זרועין ועומדים לא כל שכן שמע מינה לא חיילין

Come and hear: Rabbi Eliezer said to them: And just as ritually impure seeds, once one has sown them in the ground, become pure, then with regard to those which are already sown and then come into contact with impurity, should they not all the more so be pure? Similarly, vows that have been preemptively nullified should be nullified, since a husband can nullify vows after they have been taken. Learn from this baraita that according to Rabbi Eliezer preemptively nullified vows do not take effect at all, just as seeds that were already sown do not become impure at all.

ורבנן לא דרשי קל וחומר והא תניא יכול ימכור אדם את בתו כשהיא נערה אמרת קל וחומר מכורה כבר יוצאה אינה מכורה אינו דין שלא תימכר

The Gemara comments: And the Rabbis, do they not teach halakhot based upon an a fortiori inference of this sort? But isn’t it taught in a baraita:

Can a person sell his daughter as a maidservant when she is a young woman? You can say an a fortiori inference to show that he cannot: A maidservant who was already sold goes free upon becoming a young woman; with regard to one who has not been sold, is it not logical that she cannot be sold once she already is a young woman? This baraita shows that the Rabbis do utilize similar a fortiori inferences.