Dorothy Parker had a parrot named Onan. When asked why, she pointed to the bottom of his cage and the bird seed that had spilled on the newspaper and replied: “Because he spills his seed upon the ground!”
I was asked about the sin of Onan and the idea of contraception in Judaism. Before I could respond, my son, Ronin, posted an excellent reply going right to the point (see comments on my previous blog). Let me expand upon his insight a little.
The origin of the Mitzvah to procreate is found in בראשית Genesis 1:28, in which G commands Adam and Havah to ‘be fruitful and multiply!” This is not a negative commandment against contraception, it is a positive commandment to have kids. The reinforcement for the Mitzvah is found in the source passage for this challenge, ברשאית Genesis 38:8 with the story of Onan and Tamar. From that story comes the question about contraception. Because Onan interrupted the coitus and did not impregnate Tamar, he died, according to Torah. From this (among others) the Rabbis decided that the Mitzvah פרו ורבו to be fruitful and multiply was incumbent upon men, not women. It is therefore acceptable for women to use contraception but not for men. Yet that is only half the story. What about coitus interruptus. That has become the crux of the Onan story. Was Onan’s sin coitus interruptus? It seems clear from the text that his sin was not fulfilling his responsibility to his brother’s line by consummating the Levirate marriage. Nowhere else in Torah is anyone punished for any form of contraception, though they clearly existed. His obligation was to his brother’s line. By having a child with his brother’s widow, the child would be considered the son of his brother, not Onan. By refusing to impregnate Tamar, Onan was breaking the law. And yet from this text, The Rabbis decided that men cannot use contraception such as a condom or contraception methods such as not ejaculating in a woman’s vagina.
But it is not that simple. According to many sources, any form of sexual activity between a married couple is authentic with certain limitations though this is not a unanimous view.
It is clearly a מצווה עשה positive commandment in Judaism to have children. As with all Miztvot but 3 there is the caveat: it should not endanger life. In other words, if it is dangerous to the woman’s life she should not have a child.
As to ‘alternative’ sexual activities by a loving couple, I would side with those that say it is acceptable. As to ’spilling the seed’ which in some cases is a (rather less than reliable) form of male contraception, that is tricky. On the one hand, between a married woman and her husban, both of whom were virgins when they married, there is little chance of HIV. Of course one could contract HIV from a bad blood transfusion, (ח’וש Heaven forbid) and then it would be permissible as פקוח נפש for the sake of saving a life. Making love, is life affirming even if it is not done for the sole purpose of bringing life. It is a sign of love, a joining in יחוד oneness. יחידה oneness, is the highest level of the soul. We strive for it in our relationship with G and with our Bshert. Indeed there is a lovely play on words in Hebrew that speaks to this point. The word איש is man. אשה is the word for woman. Notice that there are 2 letters in common between the two words and two letters unique. The two unique letters are י and ה which are the two first letters of G’s name. The two letters in common are אש which means fire. The teaching is that there is lust between a man and a woman. But a higher level is the love that brings G into the relationship and especially the act of making love.
There are those who do not live traditionally Halachic lives and find all of this irrelevant. I would suggest to them that Halacha is not irrelevant. The Halacha process examined here promotes not just procreation it promotes love. There is love of that a couple shares. There is love of family, specifically here, a deceased brother. There is love for HaShem that we exhibit in our relationship with other people. Halacha considers the creative influence of love to be, in my opinion, the highest level of the יצר הטוב the creative will to do good.
 “Then Yehudah said to Onan, ‘Consort with your brother’s wife and enter into levirate marriage with her, and establish offspring for your brother” (38:8)
 At the end of the Mishnah of Yevamot, there is a disagreement cited between an anonymous teacher and Rabbi Yochanan ben Berukah. The anonymous teacher (whose view is accepted Jewish law) states that women are not obligated to be fruitful and multiply. In traditional Jewish law, it is a man’s duty to marry and have children, whereas a woman is free to remain childless.
 This prohibition is derived from the biblical narrative of Onan (Genesis 38:7‑10), son of Judah, who “spilled” his seed “on the ground.” Onan (second son of Judah and Shu’ah) was instructed by his father (after the death of his elder brother Er) to contract a levirate marriage with his childless sister‑in‑law Tamar. Onan avoided his fraternal duty and whenever he had relations with Tamar he would let the semen go to waste thereby avoiding effective consummation of the marriage.
 Any form of sexual relations between a married couple is considered legitimate even if it involves spilling of seed according to the Shulhan Arukh and Tur Even ha-Ezer 25:2 in accordance with Isaac ben Samuel of Dampierre (Ri, d. c. 1185) in Tosafot and Rabbi Joseph ben Ephraim Caro (Beit Yosef, 1488–1575) in the name of Asher ben Jehiel (Rosh, 1250–1327). The Rambam allowed such sexual activity but prohibited ejaculation in the context. The Zohar and later Sefer Hasidim were particularly concerned with spilling seed and prohibited it in the strongest of terms concerned with the demon children created by such acts.