Question: "What is onanism? Is onanism a sin?"
Answer: Onanism is yet another English word that has its roots in the Bible. The term itself comes from a character in the book of Genesis. Onanism, also called coitus interruptus, is the “interrupting” of sexual intercourse—specifically, the purposeful withdrawal of the penis from the vagina before ejaculation occurs. Onanism is synonymous with the “withdrawal method” of birth control; however, within Judaism, onanism is given a broad definition, encompassing withdrawal (coitus interruptus), masturbation, and any other “improper emission of seed.”
In patriarchal societies of the ancient Near East, the uninterrupted passing on of land and property from father to son was extremely important. It was so important that the Mosaic Law outlined the requirements for levirate marriage: if a married man died childless, his brother (or another family member) was obliged to marry the widow and sire a son who could inherit the dead man’s property and carry on the man’s name (Deuteronomy 25:5–10). The practice of levirate marriage was understood and accepted by the Israelites far earlier than the giving of the Law, and we have an example of it in Genesis 38; that’s where we find the story of Onan and his onanism.
Judah’s son Er was killed by God for his evil lifestyle, and, since Er had not fathered a son, Er’s wife, Tamar, followed the tradition of levirate marriage and married his next-oldest brother, Onan. Onan was willing to have sex with Tamar, but he wasn’t willing to sire a son with her—a son who would not legally be his and who would take away his chance of inheriting his dead brother’s property. So, in the midst of sexual relations with Tamar, Onan withdrew and “spilled his semen on the ground” (Genesis 38:9). In this way Onan ensured he would not provide a child to Tamar, even though it was his “duty” to do so (verse 8). Genesis 38:10 says, “What he did was wicked in the LORD’s sight; so the LORD put him to death also.”
The word onanism is, therefore, an eponym, since it is derived from the personal name of an individual. Onan’s action of “spilling his seed” rather than impregnating his wife is now called “onanism.” Historically, there has been a great amount of confusion about Onan’s sin. Contrary to what some teach, his sin was not masturbation. Nor is Genesis 38 teaching that the withdrawal method of birth control is sinful. No, the sin of Onan was his greedy, selfish refusal to sire a son on behalf of his brother. Onan was of the tribe of Judah, the kingly tribe and the tribe of the Messiah. In fact, Tamar, the woman wronged by Onan, is listed in the genealogy of Christ (Matthew 1:3). God had a vested interest in Tamar’s children and Judah’s grandchildren.
Is onanism a sin? The true crime of Onan was refusing to sire a son on his brother’s behalf, which doesn’t really apply to modern culture, anyway. The debate over masturbation has been thoroughly discussed elsewhere. Onanism for the purposes of birth control is fine biblically but not very effective physically—effectiveness rates vary from 96 to 73 percent. Therefore, the question of onanism’s morality does not really apply to us today.