Do one's thoughts of divorce without verbal expression make it effective? For example, when one says to himself, ''If my wife does so and so, she will be divorced,'' with the intention of effecting divorce. What will be the case if she indeed does?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

Mere thoughts are overlooked under Sharee‘ah unless one verbally expresses them.  Abu Hurayrah narrated that the Prophet said: “Allaah Overlooks one's thoughts unless he utters [them] or puts [them] into practice.” [Al-Bukhari and Muslim]

 Al-Bukhari quoted Qataadah, as saying that inward divorce is nothing.

But if one verbally expresses divorcing his wife, resolving to do so and not giving a mere promise of divorce, then his wife is divorced once she does what he made divorce conditional on. In this case, it is not conditioned that he addresses his wife, or any other person, concerning the divorce.

Allaah Knows best.