A more thorough explanation:

Definition: The bum-marriage doctrine is a principle that states that the marital-witness privilege cannot be claimed by a partner in a marriage that is practically over, even if it is still legally valid. This doctrine is also known as the moribund marriage doctrine.

Example: If a couple is separated and living apart, but not yet legally divorced, and one partner is called to testify in court against the other, they cannot claim the marital-witness privilege. This is because their marriage is considered to be practically over, and the privilege only applies to couples who are still in a valid and functioning marriage.

Explanation: The bum-marriage doctrine is based on the idea that the marital-witness privilege is intended to protect the sanctity and privacy of a functioning marriage. If a marriage is no longer functioning, then there is no longer a need to protect it. Therefore, the privilege cannot be claimed in cases where the marriage is practically over, even if it is still legally valid.