Shun sexual immorality! Every sin that a person commits is outside the body, but the sexually immoral person sins against the body itself. 1 Cor. 6:18

For out of the heart come evil intentions, murder, adultery, sexual immorality, theft, false witness, slander. Matt. 15:19

Put to death, therefore, whatever in you is earthly: sexual immorality, impurity, passion, evil desire, and greed (which is idolatry). Col. 3:5

Fornication is an odd word. The Bible is quite clear that fornication is a bad thing. If you look in the Bible for a definition of it, though, you’ll come up empty-handed. 

Most modern Bibles now use the phrase “sexual immorality” instead of fornication, since it’s slightly clearer language. But if you want to know what kind of behavior is sexually immoral, that phrase isn’t much more help! 

Some people will tell you that they know exactly what fornication is – it’s any sexual activity between two people who aren’t married. In fact, these people will often tell you that everyone, everywhere, has known that fornication is unmarried sexual activity, and anyone saying otherwise is just looking for an excuse to sleep around. Leaving aside the question of when exactly activity becomes sexual (kissing is a sexual behavior, after all, but few people think premarital kissing is a sin!), there is a bigger problem with this view, which is that it just isn’t true. Plenty of societies throughout history have not equated unmarried sex with wrongdoing. In fact, a few centuries ago in America, it was generally accepted that a couple could begin sleeping together when they had become engaged. This is actually where the practice of engagement rings came from; by giving a woman an expensive piece of collateral, the man was promising that he was committed to her and would not abandon her after they slept together. (1) Even in a society very similar to our own, views of fornication are far more diverse than some would have you think. 

The biggest problem with this view, though, is even more basic: the Bible never actually says that fornication is the same thing as unmarried sex. In fact, most biblical passages that directly deal with fornication are so-called “vice lists” in which the speaker gives us a list of bad things to avoid without elaborating on what any of them are. Even looking back at the original Greek doesn’t provide many clues. Fornication is used to translate the Greek word porneia, which is a catch-all word to describe any kind of immoral sexual activity. In other words, the Greek porneia is just as broad as the English “sexual immorality” – and just as unhelpful if you want to know exactly what these immoral behaviors are. 

The picture gets even more complicated: sometimes, the Bible says that fornication happens between a married couple.

In Numbers 25, the Israelites who are currently en route to the promised land have a big problem. Many of their men have married foreign women, who are influencing them to commit idolatry – the worship of false gods instead of the one true God. This action is described as “fornication,” and Greek translations of the Old Testament render it as porneia. (2) Now, clearly the problem here is not that the Israelite men are having unmarried sex – these women are their wives! The problem is that their sexual relations are causing them to become unfaithful to God. Their marriages tempt them to betray their values. 

A similar case of married fornication happens in the New Testament. In 1 Corinthians 5, Paul learns with horror that there is “sexual immorality (porneia) among [the Corinthians] that is not found even among gentiles, for a man is living with his father’s wife” (v. 1). The key phrase here is that this man is “living with” his father’s wife. (3) We do not know whether the son and wife were formally married, or whether they had entered into a common law marriage or cohabitation arrangement. They do, appear, to have been living in a marriage-like arrangement, and yet their sin is still fornication. St. Paul condemns their union for the same reasons that people across history have condemned incest: it damages and distorts intimate family relationships, and often leads to the exploitation of one or both members. 

Alright. So sometimes sex between married people can be fornication. Where does that leave sex between unmarried people? Does the Bible ever say that unmarried sex can be alright? 

The answer is complicated. The Bible never comes out and says that unmarried sex can be alright. However, the Bible does present several cases of unmarried sex that it does not condemn, and that seem to even be celebrated. The most famous of these cases is in the book of Ruth. Ruth is a single widow trying to provide for her mother-in-law, Naomi. Ruth begins working in the fields of a wealthy farmer named Boaz, and they strike up a relationship. The Bible tells us that Ruth “uncovered his feet” one night (Ruth 3:4), which is a Hebrew euphemism for sexual activity. The Bible doesn’t comment on Ruth’s actions directly. However, the book of Ruth generally portrays her as a faithful, loving woman. Her story ends happily; she and Boaz are married and she becomes the ancestor of the great King David. There is no condemnation of her premarital sex to be found here. 

In a similar but more complicated story, Genesis 38 relates the tale of Judah and Tamar. Tamar is Judah’s daughter-in-law. After her husband’s death leaves Tamar widowed, her brother-in-law Onan is required by law to sleep with her to give her a son. However, Onan declines to impregnate her (4) and dies without leaving her a child. Judah, now having lost two sons who married Tamar, refuses to give her his third son in marriage. 

Tamar needed children for the same reason that most ancient people needed children: the harsh conditions of ancient history were almost impossible to survive unless you had children to help you. So Tamar tricks Judah by dressing up as a prostitute. Judah sleeps with her, and she becomes pregnant. When she reveals to Judah that he is the father of her child, Judah says, “She is more righteous than I, since I wouldn’t give her to my son” (Gen 38:26). 

Now, there are some things in this story that are obviously not right. Deceiving other people is not a good thing, especially in a sexual relationship. The sexual relationship between Judah and Tamar probably makes your skin crawl. Although in the Bronze Age a relationship between father-in-law and daughter-in-law would not usually have been considered incestuous, it usually is today - and probably was considered as such in early Christianity too. What is remarkable about this story, however, is that Tamar is not condemned for her extramarital sex. Tamar is a desperate woman in desperate circumstances, and at the very least she is more righteous than Judah in how she has gone about seeking what she needs. Moreover, Tamar is mentioned later in the Bible as one of the ancestors of King David – an illustrious pedigree to possess. 

So far, I have mostly told you what fornication is not. If you are reading this article, there is a good chance you are hoping that I will tell you what fornication is. That’s the title of the article, after all, and you have a right to have your question answered. Moreover, it’s a question many people have a personal stake in. Perhaps you are considering a sexual relationship, but aren’t sure how God might view it. Perhaps you have teenage children and are wondering what to tell them about their bodies. Perhaps you have been damaged by Christian purity culture and are wondering what to hold onto and what to cast away. 

I’d like to spend the second half of this article pulling some threads together to help you with that. Certain kinds of sex acts are not inherently good or bad. Having sex is no more good or bad than extending your fist; the difference is whether you are holding a door open for someone or hitting their nose with it. Just so with sex; it is an inherently relational act, and we need to see how it will impact our relationships to know its goodness or badness. 

So what makes sex good, and what makes it fornication? To start off, look back at those Bible verses at the beginning of the article. What sort of things do Jesus and Paul group with sexual immorality? Evil intention, murder, adultery, theft, false witness, slander, greed, and impurity. Notice how almost all of these are ways of harming other people by using them as a means to an end, or by violating our commitments to others. Just so with sex. Sex becomes fornication when it damages our commitment to God or disrupts relationships with other people. Sometimes sex can be bad for us simply because we are not ready for it yet. After all, the Bible tells us that the intense passions of love can sometimes be overwhelming, especially when the beloved is not around. Therefore it says, “Do not stir up or awaken love before it is ready!” (Song 8:4). 

This citation takes us to one final biblical text that can give us insight into sex: the Song of Songs. This book is a celebration of sexual love between two people. It’s where the Bible gives us our closest look at what good sex looks like. Probably the most important factor in the Song is the characters’ praise of each other. They are in love, and like lovers throughout history, they spend most of their time telling each other how wonderful they are. The compliments are a little dated – I don’t recommend telling your lover that their stature is like the palm tree (Song 7:7) – but the feelings behind them are timeless. Each person is deeply, truly enamored of the other, and they sincerely want to tell them that. Their love is strong enough to overcome obstacles that may face them. One of my favorite passages in the Song goes like this: 

Set me as a seal upon your heart,

    as a seal upon your arm,

for love is strong as death,

    passion fierce as the grave.

Its flashes are flashes of fire,

    a raging flame.

Many waters cannot quench love,

    neither can floods drown it.

If one offered for love

    all the wealth of one’s house,

    it would be utterly scorned. (Song 8:6-7) 

Death, floods, money— all of these things are nothing in the eyes of the lovers. Their passion rivals them all, and they will seek each other even in the face of these obstacles. Their sexual union is a joyous expression of the emotional and spiritual bond they have already forged. Sex reinforces that bond. 

In so doing, it makes them the best possible versions of themselves. Let me explain. Jesus tells us that the best life is not one dominated by money or fear of death, but one marked by love. The truly good person is one who has a ceaseless desire to do good to others and to serve them. Sexual love, at its best, bonds us to another person for whom we will sacrifice and serve, even when it costs us something. (5)The physical joys of sex, pleasant though they are, are secondary to the spiritual joy of a sexual relationship. Sex at its best (6) unites our feelings and will and directs them toward another’s joy. So, good sex will make it easier for us to live the values we profess. It makes us better people. 

I want to close by talking about an essay on sexuality that I have long loved. It’s called The Body’s Grace, and it was written by Rowan Williams, the former Archbishop of Canterbury. In this essay, he talks about how sex at its best helps us see ourselves the way our lover sees us: as significant and wanted. And of course, being seen as significant and wanted is a very good thing! But there is an inevitable risk associated with it. To be seen as significant and wanted, I first have to be seen. There is a real risk that my lover will look upon me with boredom or even disgust, and instead of feeling grace I will feel profound pain. Nor can I avoid this risk by only sleeping with someone I have known for years. There is always a risk that my partner will one day grow tired of me, or will be repulsed by my graying hairs or wrinkling skin. 

I believe that most of what the Bible calls fornication is what Rowan Williams would call an attempt to avoid that risk. I can have keep sex partners at arms’ length, telling myself that if I do not care about my partner, I will not care how they see me. I can hide my faith commitments from my spouse so that they will not reject me. I can principally or even exclusively pursue my own gratification instead of a mutual love on equal terms. All of these are bad choices that will damage me and those unfortunate enough to be my sexual partners. 

On the other hand, if I choose to venture the risk of being seen by choosing sexual partners in mutually caring relationships—if I commit to keeping the promises I have made, earnestly expressing my feelings for them and receiving theirs for me, and seeking my partner’s good alongside my own—then something miraculous can happen. For as I see their desire for me, it sparks an even deeper desire for them. As they see this, their desire for me will increase, and the cycle begins anew. This escalating ecstasy of love, Williams says, is a pattern of God’s love for the world. God sees us as inimitably desirable, and so we come to love and desire God all the more for it. 

Fornication is the kind of sex that deforms us into less caring, less loving people. Good sex is the kind of sex that can make us better. It can show us in a special way what our relationship with God is like. An orgasm is a beautiful thing, but sex has far more beautiful things to show us than that. If we are willing to take on the risk of intimacy, we may know joys beyond telling – joys that make the risk of love worth it, no matter the cost. 

1. See Coontz, Stephanie. Marriage, a history: How love conquered marriage. Penguin, 2006.

2. Remember that most early Christians read Greek; even many Jews of the period didn’t read Hebrew. So most early Christians were reading the Bible in its Greek translation, known today as the Septuagint. That is why the Greek translation can give us important clues as to what early Christians thought fornication was – and wasn’t.

3. We don’t know if this woman was the man’s mother or stepmother; in either case, St. Paul is clear that it violates standards of sexual decency.

4. Onan spills his semen on the ground when sleeping with Tamar. This is why masturbation is sometimes referred to as onanism. Some Christian traditions view the waste of semen as a sin, including Roman Catholicism, but this is a very controversial topic.

5. Of course, I am not suggesting that it is good to always serve our partner and never be served in return! That is a codependent relationship, which is an obstacle to true intimacy.

6. I should mention that not all good sex will be sex at its best! We are human, and perfection is impossible for us to achieve. I simply aim to point at the kind of sexual relationship we aspire to, but we also need to recognize that in real life, commitment, mutuality, trust, etc. are never perfect whether a relationship is five days old or fifty years old.