Irreconcilable differences is New Jersey's "new" cause of action for divorce, effective 2007. This is a "true" no-fault cause, because it doesn't require a lengthy separation. It only involves telling the court in your complaint for divorce that you realized, at least six months ago, that your marriage was not working out and you don't believe it's savable. You don't have to blame your spouse for the demise of your marriage.
New Jersey's Other No-Fault Cause of Action
Before 2007, New Jersey's only no-fault grounds was an 18-month separation. Irreconcilable differences didn't replace this cause of action -- the 2007 legislative change simply added irreconcilable differences to the family law code -- so you can still use a separation cause of action if you choose to. Like irreconcilable differences, it doesn't involve casting blame on your spouse for the end of your marriage. However, you and your spouse must actually have lived in two different residences for the entire 18 months.
Extreme cruelty is the most frequently used fault cause of action in New Jersey. It can potentially affect issues of custody if your spouse's behavior was bad enough, and many spouses use it for this reason. Extreme cruelty involves domestic violence as well as mental abuse. You must wait three months after the last time your spouse hurt you to file for divorce on this cause of action, but you don't have to continue living in the same household. You must list examples of your spouse's cruel behavior in your complaint for divorce.
You must live in New Jersey for one year before filing for divorce -- unless your spouse committed adultery. The state waives its residency requirement for this cause of action, but if your spouse denies the adultery, you'll have to prove it to the court. Circumstantial evidence is acceptable. You don't have to catch your spouse in the act. If you know who your spouse strayed with, New Jersey requires you to name the individual as a "correspondent" in your divorce complaint and serve the person with a copy of the complaint. A correspondent has the right to defend against your accusation.
Other Fault Causes of Action
New Jersey also recognizes a few other fault causes of action. They include mental illness on the part of your spouse, but your spouse must be institutionalized for at least two years before you can use this grounds. If your spouse is incarcerated for 18 months, this is a cause of action as long as you don't live together after his release from prison. Desertion of one year is a cause of action, and it can be either literal -- your spouse moved out of your home -- or sexual. Sexual desertion involves a refusal to maintain a marital relationship with you, against your wishes. Drug or alcohol addiction is also grounds for divorce in New Jersey if it lasts a year or more without an attempt at recovery.