A more thorough explanation:

MATRIMONIUM NON JUSTUM

Matrimonium non justum is a Latin term used in Roman law to refer to a marriage between two people, one or both of whom do not have the legal capacity to wed. Children born from such a marriage are considered legitimate but are not under the control of the father.

An example of matrimonium non justum would be a marriage between a brother and sister, or a marriage between a person who is already married and another person. In both cases, the marriage is not legally valid because it violates the laws of conubium, which is the legal capacity to wed.

Another example would be a marriage between a minor and an adult. In Roman law, a minor did not have the legal capacity to wed, so any marriage between a minor and an adult would be considered matrimonium non justum.

Matrimonium non justum refers to a marriage that is not legally valid because it violates the laws of conubium. This means that the marriage is not recognized by the law, and any children born from such a marriage are not under the control of the father. The examples illustrate how certain types of marriages are not legally valid and are considered matrimonium non justum.