A thesis committee (or, at some universities, specifically for the doctorate, a dissertation committee), is chosen by the student in conjunction with his thesis advisor. The members, which usually vary in number from two to four, are Doctors in their field and will have the task of reading the dissertation, making suggestions for changes and improvements, and sitting in on the defense. The defense is the last hurdle in the attainment of a doctorate. At this final meeting, the doctoral candidate typically speaks for some amount of time on the dissertation, and then answers the questions of the members of the committee. At many universities, the candidate's talk is is open to the public, who may ask questions, but are then asked to withdraw so that the committee may ask further questions in a closed session. (In the the UK the defense is known as a viva, short for viva voce, Latin for "live voice".) If the defense is successful, the committee members and advisor sign the dissertation. The thesis committee can also require that final changes be made before the dissertation may be submitted to the graduate school. It is customary in many schools to grant the title of "Doctor" immediately following a successful defense by offering the words "Congratulations, Doctor..."