In California there are two grounds for a no-fault divorce. (1) Irreconcilable differences, which have caused the irremediable
breakdown of the marriage; or (2) Incurable insanity. [California Family Codes Section 2310-2313.

Irreconcilable differences are those grounds which are determined by the court to be substantial reasons for not continuing the marriage and which make it appear that the marriage should be dissolved. 

A marriage may be dissolved on the grounds of incurable insanity only upon proof, including competent medical or psychiatric testimony, that the insane spouse was at the time the petition was filed, and remains, incurably insane.  A dissolution of marriage granted on the grounds of incurable insanity does not relieve a spouse of alimony support if the court so orders.

The California approach to divorce is very liberal. California has adopted the concept of “insupportability” of “the legitimate ends of the marriage.” This is normally interpreted to mean one of the spouses can no longer live as man and wife with the other spouse, and, as such, is entitled to obtain a divorce.

What is a "no fault" divorce?

"No fault" divorce describes any divorce where the spouse suing for divorce does not have to prove that the other spouse did something wrong. All states allow divorces regardless of who is at "fault."

To get a no fault divorce, one spouse must simply state a reason recognized by the state. In most states, it's enough to declare that the couple cannot get along (this goes by such names as "incompatibility," "irreconcilable differences" or "irremediable breakdown of the marriage"). In nearly a dozen states, however, the couple must live apart for a period of months or even years in order to obtain a no fault divorce.