The Talmud relates two incidents involving a Torah scholar's using the honor due to Torah for his own purpose. One is in our gemara and it concerns Rabbi Tarfon. The other is in Mesechta Bava Kama (59b) and its hero is the Sage Eliezer Zeira. Let us relate the two and compare them.

When the harvest of fig trees is over, the owners of the fig trees relinquish ownership of whatever insignificant fruit remains and everyone has a right to take them. Rabbi Tarfon availed himself of this privilege in one field. To his misfortune, however, the owner of that field had long been the victim of robberies of grapes from his field, and when he saw Rabbi Tarfon, whom he did not recognize, he assumed that he was the thief. He put the sage in a sack and threatened to throw him in the river. Afraid that his captor might indeed carry out his threat Rabbi Tarfon cried out: "Woe to Tarfon that this fellow is killing him!" Realizing that this was the Sage Rabbi Tarfon, the field owner dropped the sack and fled in shame.

All of his life Rabbi Tarfon felt regret about his behavior and opined, "Woe to me that I exploited the Crown of Torah!"

Even though Rabbi Tarfon was perfectly entitled to the fruit he had taken, and certainly he had no obligation to pay for all the stolen grapes in order to save himself, he nevertheless felt guilty, for he was a man of great wealth and should have offered money for his release rather than exploit his status as a Torah scholar for this purpose.

Eliezer Zeira's story begins with his standing in the marketplace of Nehardeah wearing black shoes, which in those times were worn as a sign of mourning. When asked by officials of the Reish Galuta (Exilarch) to explain this public display of mourning, he declared that he was in mourning for the destruction of Jerusalem. Since they assumed him to be only a common Jew, his action was looked upon as a flagrant display of arrogant pretentiousness in practicing public mourning for Jerusalem, an act reserved for Torah scholars only. When they arrested him, he protested that he was indeed a Torah scholar. To prove his claim he offered either to answer any question in Torah which they would ask him or to pose a question to them. He was invited to pose the question and he succeeded in stumping them and supplying his own answer. When his answer was corroborated by the Sage Shmuel, he was vindicated and freed.

Why was it any more proper for Eliezer Zeira to utilize his status as a Torah scholar to save himself from prison than it was for Rabbi Tarfon to save himself from the threat of death? One answer is fairly obvious. Rabbi Tarfon had the option of saving himself with money while Eliezer Zeira did not. Maharsha adds a second solution to this problem. Eliezer Zeira was not imprisoned but rather detained until it could be established whether he had the right to publicly mourn Jerusalem. His presentation of his Torah credentials was therefore not an exploitation but a clarification which was perfectly proper.

If one wishes to annul his vow, the sage he consults must find an "opening" -- some consideration which he can present to the vow-maker as a reason for regretting that he made the vow. This can even be the consideration that by vowing to deny another Jew any benefit from his possessions he is guilty of violating the Torah prohibition of hating another Jew or taking revenge. If he declares that had he been aware of this he would not have made such a vow, the sage can declare the vow annulled.

If the consideration was not in existence at the time the vow was made, there is a dispute between Rabbi Eliezer and the majority of the Sages as to whether it is a valid opening for annulment of a vow. The classic example is that of the fellow who vows not to have any benefit from another. That other fellow then becomes a scribe whose services he now needs. Rabbi Eliezer sanctions an opening based on his declaration that had he known that fellow would become a scribe he would not have made such a vow. The other sages rule this out because it is a consideration which was not possible to have had in mind at the time of the vow.

An interesting application of the above is the case of a man who was being pressured to marry his sister's daughter. He was reluctant to do so because she was unattractive, so he took a vow not to have any benefit from her. Rabbi Yishmael then took her in hand, beautified her (the gemara says that he fixed up her appearance with a gold false tooth) and presented her to the reluctant uncle. To the sage's question whether he would have made such a vow had he seen her as she now looked, the uncle replied in the negative. Rabbi Yishmael annulled the vow.

One approach in the commentaries is that Rabbi Yishmael concurred with the view of Rabbi Eliezer, that even a consideration born after the vow was made can serve as a valid opening; thus, even if she was indeed unattractive at the time of the vow, her subsequent beautification can be grounds for regret and annulment. Another view is that if it was possible to beautify her then, she was never really unattractive and the vow was made in error. This is indicated in the words of Rabbi Yishmael following this incident: "Jewish girls are beautiful, and it is only their poverty which renders them unattractive."

Nedarim 66a