פרו ורבו Understanding the Mitsvah to be Fruitful and Multiply

Essential Questions:

  1. How might a deep understanding of halakhah help us solve real world problems?

  2. How does the halakhic system take into account human needs and desires?

  3. How might new technologies impact our observance of halakhah?

  4. How might we make good decisions when a halakhah governs something that is in many ways beyond our control?

Desired Results:

  1. Learners will understand the scope and content of the mitsvah of פרו ורבו.

  2. Learners will get a taste of how halakhah develops and is applied to real world situations.

Learning Outcomes:


  1. Learners will be able to articulate the scope of the mitsvah of פרו ורבו: Is it giving birth to children? Raising children? Having multiple generations of descendants? How exactly do you know if and when you’ve fulfilled this mitsvah? How do different sources answer these questions?

  2. Learners will synthesize halakhic knowledge and human sensitivity to answer real world questions about the observance of halakhah.

  3. Learners will understand how halakhah responds to technological innovation and change.

Skills and Abilities:

  1. Learners will be able to complete a targeted halakhic research project, and answer questions such as: What are acceptable sources? How do I find them? What tools do I need in order to access, read, and understand them? Who are the halakhic experts in my world who I can turn to for assistance?

  2. Learners will improve their ability to read and understand a sugya in the Gemara (with some scaffolding).

  3. Learners will be able to investigate the halakhic ramifications of a sugya.

Learning Activities: [Teachers may elect to do some or all of these activities, depending on the class level and time allotted]

1) What do the students know or believe? Begin with a Group Level Understanding (GLU) assessment to check for understanding. There are many ways to do this (see here for more information on GLU/GLA) and here is one possible set of instructions. This will allow you to get a sense of what students know or believe about this mitsvah prior to this unit.

2) Learn the Gemara: The students will then learn the sugya in Yevamot about פרו ורבו. The Mishnah and the most relevant section of the Gemara are below (a more advanced class could also do the section of the Gemara that immediately follows the Mishnah). Note that in this setting, students learn Gemara in hevruta pairs during class time, and also work on the text independently or with their hevruta at home. The homework allows for a flipped classroom model, in which the basics of the text are mastered outside of the classroom, freeing up class time for troubleshooting and higher-level conversations. The scaffolded learning guide is here (the guide for the Mishnah is here), and the homework assignment with embedded video is here.

מתני׳ לא יבטל אדם מפריה ורביה אלא א"כ יש לו בנים ב"ש אומרים שני זכרים וב"ה אומרים זכר ונקבה שנאמר (בראשית ה, ב) זכר ונקבה בראם:

MISHNA: A man may not neglect the mitzva to be fruitful and multiply unless he already has children. Beit Shammai say: One fulfills this mitzva with two males, and Beit Hillel say: A male and a female, as it is stated: “Male and female He created them” (Genesis 5:2).

בית שמאי אומרים שני זכרים: מאי טעמייהו דבית שמאי ילפינן ממשה דכתיב (דברי הימים א כג, טו) בני משה גרשום ואליעזר ובית הלל ילפינן מברייתו של עולם ובית שמאי לילפי מברייתו של עולם אין דנין אפשר משאי אפשר ובית הלל נמי לילפו ממשה אמרי לך משה מדעתיה הוא דעבד דתניא שלשה דברים עשה משה מדעתו והסכימה דעתו לדעת המקום פירש מן האשה ושיבר הלוחות והוסיף יום אחד פירש מן האשה מאי דרש אמר ומה ישראל שלא דברה עמהם שכינה אלא לפי שעה וקבע להם זמן אמרה תורה (שמות יט, טו) אל תגשו אל אשה אני שמיוחד לדבור בכל שעה ושעה ולא קבע לי זמן על אחת כמה וכמה והסכימה דעתו לדעת המקום שנאמר (דברים ה, ל) לך אמור להם שובו לכם לאהליכם ואתה פה עמוד עמדי שיבר את הלוחות מאי דרש אמר ומה פסח שהוא אחד משש מאות ושלש עשרה מצות אמרה תורה (שמות יב, מג) כל בן נכר לא יאכל בו התורה כולה וישראל מומרים על אחת כמה וכמה והסכימה דעתו לדעת המקום דכתיב (שמות לד, א) אשר שברת ואמר ריש לקיש אמר ליה הקב"ה למשה יישר כחך ששברת הוסיף יום אחד מדעתו מאי דרש דכתיב (שמות יט, י) וקדשתם היום ומחר היום כמחר מה מחר לילו עמו אף היום לילו עמו ולילה דהאידנא נפק ליה ש"מ תרי יומי לבר מהאידנא והסכימה דעתו לדעת המקום דלא שריא שכינה עד שבתא תניא רבי נתן אומר ב"ש אומרים שני זכרים ושתי נקבות ובה"א זכר ונקבה א"ר הונא מ"ט דרבי נתן אליבא דב"ש דכתיב (בראשית ד, ב) ותוסף ללדת את אחיו את הבל הבל ואחותו קין ואחותו וכתיב (בראשית ד, כה) כי שת לי אלהים זרע אחר תחת הבל כי הרגו קין ורבנן אודויי הוא דקא מודית תניא אידך ר' נתן אומר ב"ש אומרים זכר ונקבה ובה"א או זכר או נקבה אמר רבא מ"ט דר' נתן אליבא דב"ה שנא' (ישעיהו מה, יח) לא תהו בראה לשבת יצרה והא עבד לה שבת

§ The mishna states that Beit Shammai say that one fulfills the mitzva to be fruitful and multiply when he has two males. The Gemara asks: What is the reason of Beit Shammai? The Gemara answers: We learn this from Moses as it is written: “The sons of Moses, Gershom and Eliezer” (I Chronicles 23:15). Since Moses did not have any other children, two sons must be sufficient to fulfill the mitzva. And the reason of Beit Hillel is that we learn from the creation of the world, as mankind was created male and female. The Gemara asks: And Beit Shammai, let them learn from the creation of the world as well. The Gemara answers that Beit Shammai could say to you: We do not derive a case where it is possible from one that is not possible. Mankind was initially created with a male and female because otherwise reproduction would not have been possible. However, this fact cannot serve as a source that the mitzva to be fruitful and multiply is fulfilled only once one has a son and a daughter. The Gemara asks: And Beit Hillel, let them also learn from Moses. Beit Hillel could say to you: Moses acted based on his own perception when he separated from his wife, but this does not mean that a man is permitted to neglect the mitzva to be fruitful and multiply after fathering two males, as it is taught in a baraita: Moses did three things based on his own perception, and his perception agreed with the perception of the Omnipresent: He separated from his wife, he broke the tablets, and he added one day to the days of separation before the revelation at Sinai. The Gemara clarifies: When Moses separated from his wife after the revelation at Sinai, what did he interpret that led him to do so? He said: If in the case of Israel, with whom the Divine Presence spoke only temporarily and for whom God set a specific time for revelation, the Torah stated: “Do not approach a woman” (Exodus 19:15), I, Moses, who am set aside for divine speech all the time and for whom God did not set a specific time, all the more so I must separate from my wife. And his perception agreed with the perception of the Omnipresent, as it is stated after the revelation at Sinai: “Go say to them: Return to your tents; and you, stand here with Me” (Deuteronomy 5:26–27). This indicates that whereas others could return to their homes and normal married life after the revelation at Sinai, Moses was to stay with God and not return to his wife. Moses broke the tablets following the sin of the Golden Calf. What did he interpret that led him to do so? Moses said: If in the case of the Paschal lamb, which is only one of 613 mitzvot, the Torah states: “No alien shall eat of it” (Exodus 12:43), excluding not only gentiles but apostate Jews as well, then here, in the case of the Golden Calf, where the tablets represent the entire Torah and where the Jewish people are apostates, as they are worshipping the calf, all the more so must they be excluded from receiving them. And his perception agreed with the perception of the Omnipresent, as it is written: “The first tablets that you broke [asher shibbarta]” (Exodus 34:1), and Reish Lakish said: The word asher is an allusion to the fact that the Holy One, Blessed be He, said to Moses: May your strength be true [yishar koḥakha] that you broke the tablets. When Moses added one day to the days of separation before the revelation at Sinai based on his own perception, what did he interpret that led him to do so? He reasoned that since it is written: “And sanctify them today and tomorrow” (Exodus 19:10), the juxtaposition of the words “today” and “tomorrow” teaches that today is like tomorrow: Just as tomorrow the men and women will separate for that day and the night preceding it, so too, today requires separation for the day and the night preceding it. Since God spoke to him in the morning, and the night of that day already passed, Moses said: Conclude from this that separation must be in effect for two days aside from now, i.e., not including the day of the command. Therefore, he extended the mitzva of separation by one day. And his perception agreed with the perception of the Omnipresent, as the Divine Presence did not rest upon Mount Sinai until Shabbat morning, as Moses had determined. § It is taught in a baraita that Rabbi Natan says that Beit Shammai say: The mitzva to be fruitful and multiply is fulfilled with two males and two females. And Beit Hillel say: A male and a female. Rav Huna said: What is the reason of Rabbi Natan, in accordance with the opinion of Beit Shammai? It is as it is written: “And again she bore his brother [et aḥiv] Abel [et Hevel]” (Genesis 4:2). The use of the superfluous word “et” indicates that she gave birth to Abel and his sister, in addition to Cain and his sister. And it states: “For God has appointed me another seed instead of Abel; for Cain slew him” (Genesis 4:25). This indicates that one must have at least four children. And the Rabbis, how do they understand this verse? In their opinion, Eve was thanking God for granting her another child, but one is not obligated to have four children. It is taught in another baraita that Rabbi Natan says that Beit Shammai say: The mitzva to be fruitful and multiply is fulfilled with a male and a female. And Beit Hillel say: Either a male or a female. Rava said: What is the reason of Rabbi Natan in accordance with the opinion of Beit Hillel? It is as it is stated: “He did not create it a waste; He formed it to be inhabited” (Isaiah 45:18), and one has made the earth inhabited to a greater degree by adding even one child to the world.

3) Check for understanding: Review the sugya in class, using selected questions from the learning guide to ensure that the students comprehend the text and are able to begin thinking about the big ideas.

4) How might we find halakhic resources? Check for prior knowledge, and show the students how to find halakhic resources on Sefaria. Below are screen shots of some ways you might choose to demonstrate Sefaria’s abilities to your students.

Option 1: Start from the verse in Genesis (or, if you prefer, from the Talmud in Yevamot) that commands procreation, and demonstrate how to use Sefaria’s sidebar to find relevant resources.

Option 2: Try searching “procreation” (or פרו ורבו, or related terms) on Sefaria.

Discuss how they might trace modern halakhic works that they find elsewhere online back to the original sources, by pursuing footnotes and references on Sefaria.

Ask: Have you ever asked a halakhic question to an expert? Who did you ask? How did you choose that person? What makes an answer good or useful? The teacher may want to have one or two examples in mind to share with students.

5) You be the posek: Assign the students to write teshuvot (halakhic responsa). Each pair/group of students is assigned one of the questions on this assignment sheet. Using Sefaria, each hevruta is expected to do research, write up their answer, and create a daf mekorot, a source sheet, to support their answer.

6) Get the community involved: Sefaria makes it easy to share and showcase materials. Here are some possibilities for getting the larger community engaged in this project.

  • Invite a panel of experts, and have the students present their answers.

  • Create a public group that functions as a digital gallery of their materials. Invite experts in any location to contribute to the group and/or respond to the students’ materials.

  • Invite members of the school community to view the public group and appreciate all of the hard work the students invested.

Assessment evidence:

  • Responses in worksheets (spot checked by teacher as students work in hevruta)

  • Homework answers

  • Participation in class discussions (are students engaged, etc.)

  • Quality of teshuvot (here is a sample rubric; adjust to suit your version of the assignment)

  • Conversation with local experts / non-local experts (ask the expert how they experienced the conversation)

  • Public group / digital gallery - quality of submissions (this is part of the rubric)

  • Do a second round of GLA/GLU process at the end of the unit. What do the students report having learned? Did they have a good experience?

Possible interdisciplinary connections:

  • Biology class: Understanding different types of ART (assisted reproductive technologies), and/or the biological causes of different types of infertility.

  • Medical ethics: Invite an expert from a local medical center to come speak to the class, or arrange for a videoconference with someone who is not local.

  • Tanakh: Which characters in the Bible struggle to have children? What responses are offered within the text? What might this teach us about the context for the mitsvah of פרו ורבו?