The Sin of Onan and Contraception

Our thesis is that the story of Onan in Genesis chapter 38 offers scriptural and logical grounds for believing that contraceptive acts are sinful. We set out a five-part modus ponens argument which considers the meaning and significance the story of Onan and, by showing that contraceptive acts are substantially similar to the act for which Onan is infamous, conclude that Christians ought not to practise contraception. We then respond to objections to this conclusion before finally and briefly touching upon some of the implications of our thesis for Christian ethics, namely with reference to the perverted faculty argument and natural law.