What Evidence Is Needed to Prove Adultery?

Though there may be slight differences in the legal definition of adultery among different states, adultery occurs when a husband or wife has consensual sexual relations with someone outside of the marriage. Some states also require that sexual intercourse take place between a man and woman for the relationship to be considered adulterous, and in nearly every state, a failing marriage is not a legal defense against adultery.

Direct evidence is the most effective way for you to prove adultery and obtain a successful divorce. Direct evidence is firsthand proof that clearly displays the adultery in a way that is in incontrovertible. An eyewitness account is one example of direct evidence. You must find someone willing to testify or sign an affidavit that they observed your spouse having sexual relations with another person. Another example is photographs that show your spouse in the act of having sexual relations with another person. Because of the private nature of this kind of proof, direct evidence is very hard to obtain.

Circumstantial evidence is indirect evidence that suggests that something is likely to have occurred, but leaves a certain amount of doubt because there is no witness to support the evidence. Circumstantial evidence uses the preponderance of a specific set of circumstances to draw conclusions. In the case of adultery, circumstantial evidence would be photographs that show your spouse and another man holding hands at a restaurant, kissing at a public park, or emerging from a hotel together. Though you wouldn't be able to definitively say they had sexual relations, you can infer from the evidence that they are romantically involved, which in turn can reasonably lead you to believing they are engaging in sexual intercourse as an expression of that romance.

More than 20 states still have adultery laws, though these cases are rarely brought to trial. These laws are reminders that the United States used to treat infidelity as a moral sin punishable by the government. In Minnesota, there is a law that prohibits married women from having affairs, and another law that criminalizes a single woman who has sex. If the married woman is found guilty of adultery, she faces a prison sentence or a fine not to exceed $3,000, or both.