If a man who had yet to fulfill the Misva of Peru U’r’bu (procreation) marries a woman who is incapable of bearing children, he is required by Torah law to divorce this woman so he can marry a childbearing woman and fulfill his obligation. The Rama (Rabbi Moshe Isserles of Cracow, 1525-1572) writes that he may even divorce the woman against her will. Although Rabbenu Gershom (10th-11th century) issued a famous ban against divorcing one’s wife unless she agrees to the divorce, this ban does not apply if a man has not fulfilled his Misva of Peru U’r’bu and his wife cannot bear children. The Rama adds, however, that nowadays Bet Din does not have the authority to force the husband to divorce the wife (listen to audio recording for precise citation).
If a person devotes himself to full-time Torah study, and he fears that after marriage the responsibilities of supporting a family will not allow him sufficient time for serious Torah learning, then he may delay marriage. Of course, he must get married and have children, but he is allowed to delay marriage so he can devote himself to intensive Torah study. This is on condition that he is, indeed, seriously involved in intensive Torah learning, and, secondly, that his Yeser Ha’ra (evil inclination) has not overcome him.
There is a dispute among the Halachic authorities as to whether a person fulfills the Misva of Peru U’r’bu by adopting and raising an orphan boy and orphan girl. According to all views, however, if a person had a son and daughter who passed away, he can fulfill the Misva by adopting and raising an orphan boy and an orphan girl.
Even after a person has fulfilled the Misva of Peru U’r’bu, it is a Misva for him to be married. According to the Rif (Rabbi Yishak of Fez, Morocco, 1013-1103), it is forbidden on the level of Torah law for a person to willingly remain unmarried, whereas according to the Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), this is forbidden by force of Rabbinic enactment.
If a person has a son and a daughter and they did not get married, or if the daughter did not get married and the son married an infertile woman, the father has fulfilled his obligation of Peru U’r’bu, even though his children are not reproducing.
If a non-Jew had children, and then he and his children converted and became Jews, the father has fulfilled his Misva of Peru U’r’bu. This does not apply, however, in the case of an Ebed Kena’ani (a gentile servant of a Jew). Halacha does not consider the children of an Ebed Kena’ani as his offspring, and therefore even if he and his children convert and become Jewish, he has not fulfilled his Misva of Peru U’r’bu, since he does not have children in the Halachic sense.
Summary: A person who has yet to beget a son and a daughter may not marry a woman who is incapable of bearing children, and if he does, he must divorce her so he can marry a childbearing woman and fulfill his Misva. There is a Misva for a man to be married even after he has begotten children. A serious student of Torah may delay marriage so he can study Torah unencumbered, provided that he has control over his Yeser Ha’ra. A man who begot a son and a daughter has fulfilled the Misva even if they do not marry. A gentile who converts together with his children is considered to have fulfilled the Misva. It is questionable whether one fulfills the Misva by adopting an orphan boy and an orphan girl.
