Most states allow spouses seeking a divorce to allege fault in the breakup of the marriage as a basis for the divorce. Alleging the other spouse’s fault—rather than seeking the divorce on no-fault grounds (irreconcilable differences or incompatibility, making the marriage unsustainable)—is generally a basis for requesting the court make an uneven distribution of the marital or community property in favor of the spouse alleging the other’s spouse’s fault.

In states that allow a spouse to seek a divorce on fault grounds, the grounds that may be alleged vary from state to state, but generally include adultery, cruelty, conviction of a felony, family or domestic violence, abandonment, mental illness, and substance abuse (drugs and alcohol). Spouses may also seek a divorce on no-fault grounds in these states.

In no-fault states, a spouse is not allowed to allege fault as grounds for the divorce, and the court is not allowed to consider fault in dividing the marital or community property—but allegations of fault may be considered for other purposes, such as spousal support and child custody. No-fault states include California, Colorado, Florida, Hawaii, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, Oregon, Washington, and Wisconsin. And in some states “incurable insanity” is a no-fault ground for divorce.

The grounds on which a spouse may seek a divorce (fault or no-fault) are usually located in a state’s statutes—often in the family code or domestic relations code.

In Montana (MT), the law provides for no-fault divorce, which means that a spouse seeking a divorce is not required to prove the other spouse's fault as a basis for the divorce. The primary ground for a no-fault divorce in Montana is the irretrievable breakdown of the marriage, where spouses can assert that they have irreconcilable differences that have led to the marriage being permanently destroyed. While fault is not a required element to obtain a divorce, it may still be relevant in certain aspects of the divorce proceedings. For example, while Montana courts generally do not consider fault in dividing marital property, allegations of fault may influence decisions related to spousal support and child custody. It is important to note that the specifics of how fault impacts these decisions can vary, and an attorney can provide guidance tailored to the individual circumstances of the case.