Hi, Mr. David Hi, all
A person who talks to ............ is not necessarily mad. ( oneself - himself )
I think ONESELF is the answer. What do you think ?
Hi, Dr Ahmed—Please do not address questions to anyone in particular here, including me. Any member is welcome to reply in a given thread if he or she has something to add.
"Oneself" is not the answer; indeed, "oneself" would be ungrammatical there. For "oneself" to work, the subject would need to be changed to "one": "One who talks to oneself is not necessarily mad."
"Himself" works fine: "A person who talks to himself is not necessarily mad." As Ahmed towab points out, you can also use "himself or herself," to be more inclusive. The other choice, "him- or herself," requires a suspensive hyphen.