Two cases of half-slave, half-free people are mentioned in our gemara. One is the male Canaanite slave owned by partners and liberated by one of them, and the other is the same situation in regard to a female slave.

In the case of the male slave there is a consensus in the mishna that we compel the owner of the half still in bondage to liberate him and accept a promissory note from him as payment. The reason for this is that the half-slave will otherwise be denied the opportunity of fulfilling the mitzvah of procreation, since his unique status renders it impossible for him to marry either a free woman or slave.

In the case of the female, however, the gemara cites a precedent in which the owner of a half-slave was compelled to liberate her but rejects the suggestion that this was in order for her to be enabled to fulfill the mitzvah of procreation. The majority view of the Sages is that a woman is not obligated in this mitzvah and the reason given for liberating her is that she was being exploited for promiscuity and the only way to protect her and the public was to liberate her and enable her to marry (Gittin 43b).

Tosefot calls attention to the mishna's citing as a source for the half-slave's mitzvah of procreation the verse (Yishayahu 45:18) "He did not create (the world) to be desolate but rather to be populated" rather than the Torah command to "Be fruitful and multiply" (Bereishet 1:28). The reason given for this by the Tosefist Rabbi Yitzchak ben Mordechai is that a slave, like a woman, is also exempt from the obligation of "Be fruitful and multiply" but he is expected to fulfill the Divine plan for populating the world. Since this mitzvah relates to his entirety it is cited by the mishna rather than the Torah command which relates to only half of him.

But if the issue is populating the world, this should apply to the female slave as well, just as it applies to regular Jewish women and male slaves? True, concedes Tosefot, but we nevertheless would not compel the owner of the female half-slave to liberate her for the sake of this mitzvah if the issue of promiscuity was not involved. This is so because while we can be confident that a male slave will marry upon being liberated because he then has the Torah obligation of "Be fruitful" like every regular Jew, we do not have that confidence in the liberated female slave doing so because she will not be obligated by Torah law to "Be fruitful," since Jewish women are not thus obligated and might therefore ignore the need to fulfill the lesser mitzvah of populating the world. Without concern of promiscuity, therefore, her situation would not warrant a coerced liberation.

Gittin 41b

In the course of the gemara's discussion of the laws pertaining to a community's responsibilities for ransoming Jewish captives from their heathen kidnappers, the fascinating story of Rabbi Ilish's experience is cited.

Seated next to this sage in captivity was a man who understood the language of the birds. When a raven flew by and chirped Rabbi Ilish asked this fellow captive what the bird had said. "Ilish, flee! Ilish, flee!" he answered.

"The raven is a liar," said Rabbi Ilish, "and I cannot rely upon him."

Then a chirping dove flew by and once again the sage turned to his companion for an interpretation. "Ilish, flee! Ilish, flee!" was again the message he relayed.

"The Jewish people are compared to a dove," said the sage, "and I can safely conclude that I will be favored with a miracle."

Rabbi Ilish did indeed escape and miraculously crossed a river and safely eluded his pursuers.

The simple reading of this story indicates that Rabbi Ilish did not understand the language of the birds and was dependent on the skill of his fellow captive. One of the early commentaries, the Aruch, surprisingly concludes from our gemara that this sage did understand bird language. Rabbi Akiva Eiger, in his "Gilyon HaShas" footnotes mentions that this approach has already been challenged as being at odds with the simple reading.

An interesting defense of the Aruch's approach was offered by Rabbi Chaim Shmulevitz, the late Rosh Hayeshiva of Yeshivat Mir in Jerusalem. Rabbi Ilish certainly did understand bird language for otherwise he would not have attached any significance to their chirping. But he was also aware that his intense desire to be free might cause him to be so subjective that he might be hearing what he would like to hear rather than what was actually conveyed by the birds. He therefore turned to his companion for an objective confirmation that he was being informed by Heaven that his escape would be successful.

The difference between this sage's reactions to the messages of raven and dove is explained by Maharsha on the basis of the performance of both those birds when sent by Noach after the Deluge to test the dryness of the land. Since the raven proved unfaithful, his message was distrusted by Rabbi Ilish. The dove could be relied upon, however, and even if his companion was lying the very appearance of a dove symbolizing Jewish survival was accepted as a reliable sign to flee to safety.

Gittin 45a