In a discussion I had with an acquaintance, I was presented with the following claim: “Paul disagrees with Jesus on the circumstances of legitimate divorce.” My acquaintance was referring to Matt. 5:31-32, Matt. 19:9, and 1Cor. 7:10-11. But do these contradict? The claim is that Jesus (according to Matthew) allows for divorce in cases involving porneia, which is usually translated ‘fornication.’ But if this is a contradiction, why present it as a contradiction between Jesus and Paul? Why not between Matthew on the one side, and Mark, Luke and Paul on the other? Neither Mark (10:11-12) nor Luke (16:18) include the ‘porneia clause,’ as Matthew did, and neither does Paul. But does this present us with a contradiction?
Mark, Luke and Paul wrote, as far as I know, for a predominately Greek audience, while Matthew wrote for a predominately Hebrew audience. It has been pointed out that the Greek noun πορνεία (porneia) (Matt. 5:32, Matt. 19:9) is not the usual word for adultery, which is μοιχεύω (moichevō), and that a better translation of πορνεία would be ‘unlawful marriage,’ ‘invalid marriage’ or ‘fornication.’ The concept of an unlawful marriage was common for the Hebrew people and the Near Eastern peoples, but not for the Greek and Roman peoples. David Janzen maintains that for Christ, divorce is only persmissible with ‘just cause,’ and he “defines just cause very narrowly as porneia.” And πορνεία, Janzen points out, is here meant as “sex on the part of the woman during betrothal or marriage with a man other than her husband.”
This blog post points out that if we do a word search on the usage of πορνεία in the New Testament, we see that it generally means fornication (sex before marriage), homosexual relations, sex with your mother-in-law (or the equivalent) and incestuous relations. What Jesus, according to Matthew, seems to say, then, is this: You can only divorce your spouse if your marriage wasn’t lawful or valid in the first place, either if she (or you) was a fornicator who had given herself to another person while you were betrothed, or if she was already married, if you were a homosexual couple who couldn’t marry in the first place or if you were related (by blood or through marriage). Divorce in this instance would then be the equivalent of an annulment. I find this very plausible, especially since both μοιχεύω (the normal term for adultery) and πορνεία is used in Matt 5:32 and 19:9 as something distinct from one another, as seen, for example, in Matt. 15:19, Mark 7:21and Gal. 5:19.
This also shows us that there is not contradiction between Matthew, Mark, Luke and Paul.
 See, for instance, Matt 5:27-28.32; 19:9.
 For some scholarly treatments of the question, see Allen R. Guenther, “The Exception Phrases: EXCEPT πορνεία, Including πορνεία or Excluding πορνεία? (Matthew 5:32; 19:9)” (Tyndale Bulletin 53:1, 2002), pp.83-96 and David Janzen, “The Meaning of Porneia in Matthew 5.32 and 19.9: An Approach from the Study of Ancient Near Eastern Culture” (Journal for the Study of the New Testament 80, 2000), pp.66-80. For a ‘lighter read,’ see this blog post.