Often when asked where the Bible condemns contraception some Christians appeal to Genesis 38:8-10. There, Onan, son of Judah, is told to have intercourse with his deceased brother’s wife to “perform the duty of a brother-in-law to her and raise up offspring for [his] brother” (v.8). But knowing the offspring wouldn’t be his, Onan “spilled the semen on the ground, lest he should give offspring to his brother” (v.9). The author immediately reports that “[God] slew” Onan because of his deed. This, it’s argued, reveals that contraception is contrary to God’s will.
Recently, someone in our TikTok comment section was not convinced:
Let’s take the latter objection first—that the text only describes what happens and doesn’t give us the prescription that we ought not to contracept.
Our critic is simply wrong. The text does tell us Onan’s deed conflicted with God’s will: “And what he did was displeasing in the sight of the LORD” (v.10). Given the implied assumption for this kind of religious text that we should avoid doing what displeases God, we can conclude that the passage is prescriptive and not merely descriptive. We can derive an “ought” from this event pertaining to at least one form of contraception: spilling semen to avoid conception.
This leads me to the first objection.
Our critic is right in saying it would be fallacious to move from God’s displeasure with one form of contraception to His displeasure with all forms of contraception. Spilling semen is not the only way a couple can contracept. Since that’s the only form of contraception that the above passage deals with, the appeal to Onan’s sin would only achieve the goal of providing evidence against that specific form of contraceptive act that Onan committed. More work would have to be done, whether biblically or philosophically, to determine whether other forms of contraception (e.g., the pill) are also displeasing to God. For an introductory philosophical explanation, see my articles “Sex for Goodness Sake,” and “How Contraception Thwarts Love.”
This is not to say, however, that a Catholic who makes the above argument is blameworthy for his lack of nuance. Often, the argument is given as an answer to the basic question of whether the Bible condemns contraception without any specification as to a particular form. And for a general question like that, Genesis 38:8-10 suffices.