Doctor of Philosophy, abbreviated Ph.D. or PhD is an advanced academic degree awarded by universities. In the USA, the Ph.D. is the highest academic degree awarded by universities in many fields of study. American students typically undergo a series of three phases in the course of their doctoral work, after they have obtained a bachelor's degree. In some cases a master's degree may be required for a Ph.D. program, but in other cases (when a master's is not required) it may not be possible to fully transfer credits from a previously attended master's program to the Ph.D. program. In some fields, the master's is considered terminal, and a university's Ph.D. program may refuse to accept any graduates from the same school's master's program. The first phase consists of coursework in the student's field of study and requires one to three years to complete. This often is followed by a preliminary or comprehensive examination and/or a series of cumulative examinations where the emphasis is on breadth rather than depth of knowledge. Some Ph.D. programs require the candidate to complete successfully requirements in pedagogy (taking courses on higher level teaching and teaching undergraduate courses) and/or applied science (e.g., clinical practica and predoctoral clinical internship in Ph.D. programs in clinical or counseling psychology).Another two to four years are usually required for the composition of a substantial and original contribution to human knowledge in the form of a written dissertation, which in the social sciences and humanities is typically 50 to 450 pages in length. In many cases, depending on the discipline, a dissertation would consist of (i) a comprehensive literature review, (ii) an outline of methodology, and (iii) several chapters of scientific, social, historical, philosophical, or literary analysis. Typically, upon completion, the candidate undergoes an oral examination, sometimes public, by his or her supervisory committee with expertise in the given discipline.
As the Ph.D. is often a preliminary step toward a career as a professor, throughout the whole period of study and dissertation research the student may be required or at least offered the opportunity, depending on the university and degree, to teach undergraduate or sometimes graduate courses in relevant subjects.
The Ph.D. is often misunderstood to be synonymous with the term "doctorate". While the Ph.D. is the most common doctorate, the term "doctorate" can refer to any number of doctoral degrees in the United States. The U.S. Department of Education and the National Science Foundation recognize numerous doctoral degrees as "equivalent", and do not discriminate between them.