The highest postgraduate degree award made by a university or other institution of higher education. The degree of Doctor of Philosophy (Ph.D. or D.Phil.) is awarded following the candidate's successful completion of a thesis, which they must also successfully defend at a viva voce examination. Higher doctorates such as Doctor of Literature (D.Litt.) are awarded in acknowledgement of the recipient's body of published works. Once awarded the doctorate, the successful candidate is entitled to be called ‘doctor’ if he or she so wishes.