How Many Children?

The first mitzvah in the Torah is to have children -- "peru u-revu - be fruitful and multiply". How many children is a Jewish man obligated to (try to) have? The Mishnah and Gemara (Yevamos 61b-62a) discuss the views of Beis Shammai and Beis Hillel. According to Beis Shammai, a man is biblically obligated to (try to) have four children -- two sons and two daughters. According to Beis Hillel, and this is the view halakhah follows, it is two children -- one son and one daughter.

However, that is not the end of the story. The Gemara (Yevamos 62b) quotes the following Baraisa:
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R. Yehoshua said: [Even if] a man was married to a woman in his youth he should also be married to a woman in his old age; [even if] a man had children in his youth he should also have children in his old age, as it says "In the morning sow your seed, and at evening do not let your hands be idle" (Eccl. 11:6).

In other words, there is an obligation to continue having children even after you have fulfilled your biblical obligation of having a son and daughter. What is the strength of this obligation? It seems to be at least a rabbinic obligation, if not one with post-Mosaic biblical force (divrei kabbalah). That is how the Minchas Chinukh (1:27) describes it, although he quotes a Ramban who seems to say that it is less than that. R. David M. Feldman (Birth Control in Jewish Law, pp. 48-49) writes, "The second 'rabbinic mitzvah' is known as la-erev... Both these rabbinic expositions have the force of law and are treated in the Responsa alongside the primary biblical one, removing, in effect, its Mishnaic limitations [of one son and one daughter]".

However, I saw that R. J. David Bleich (Judaism and Healing, p. 52) writes, "According to rabbinic interpretation, the obligation with regard to procreation is fulfilled by the siring of two children, one male and one female, provided that each of the two in turn becomes the parents of a boy and a girl. Nevertheless, further procreation is regarded as meritorious" (emphasis added). R. Bleich seems to say that there is no explicit obligation to have more than two children and "In the morning sow your seed..." is not an obligation but a meritorious attitude. R. Hershel Schachter writes similarly in his classic article on birth control in The Journal of Halacha and Contemporary Society (IV [Fall 1982], pp. 17-18) and attributes this to the Arukh Ha-Shulchan (Even Ha-Ezer 1:8).

Setting that aside, I recently heard R. Schachter say something both surprising and extremely reasonable in a lecture (link - audio, starting at 9 minutes). He suggests that the biblical obligation to procreate requires having a son and a daughter, and the further meritorious act involves having another son and another daughter. In other words, it does not involve having countless children but four. This is not a maximum. As he points out, he has nine children! However, above two sons and two daughters it is a matter of preference as determined by the many issues that concern a religious personality.

(Needless to say, you should always discuss halakhic matters with your rabbi before following what you read on the internet.)