Sentence:  Chewing it over with his colleagues and in his own <WSD>mind</WSD> , he reaches a tentative identification of the question - tentative because it may change as he explores it further and because , if no tolerable answer can be found , it may have to be changed into one which can be answered . 
Meaning of the word marked with <WSD> tags:  that which is responsible for one's thoughts and feelings; the seat of the faculty of reason