A Ph.D. degree is a Doctor of Philosophy, or "philosophiae doctor" in the original Latin. "Philosophy" means love of knowledge, and a Ph.D. is the highest graduate degree in the U.S. It's available in many fields, including the humanities, social sciences, natural sciences, business and engineering. Unlike professional degrees such as medical doctorates, the Ph.D. is a research degree and typically leads to academic or research careers.

Admissions, Coursework and Exams

Some programs admit Ph.D. students after the bachelor's, while others require completing a master's degree first. Universities and disciplines vary, but students typically need approximately 54 semester hours after a master's for a Ph.D. During the first year or two, students take graduate-level courses leading to mastery of the the subject matter. These usually include required core courses plus electives in an area of special interest. After completing the coursework, students must pass comprehensive exams to advance to Ph.D. candidacy and begin original research.

Varieties of Ph.D. Research

Original research is central to any Ph.D. program, but what constitutes research varies with the discipline. For example, a Ph.D. student in English may advance a new interpretation of a particular novel, while a candidate in biochemistry may conduct experiments on how a drug functions in the body. A computer science specialist may develop new software during Ph.D. research. Whether or not the research leads to practical applications, the emphasis is on the expansion of knowledge.

Research and Dissertation

With the assistance of a faculty adviser, the candidate chooses an original research topic that will serve as a basis for the Ph.D. thesis or dissertation. In some programs, a combination of shorter papers can count as a thesis. The adviser usually chairs the student's thesis committee and meets with the student at least once a semester or as needed while the student conducts the research and writes the dissertation. When the dissertation is finished, the candidate submits it to the thesis committee and must defend it orally to receive the Ph.D.

Time to Completion

It usually takes at least four years to earn a Ph.D., according to the College Board. The time required for a Ph.D. depends in part on the particular program and on whether the student already has a master's. Other factors can extend the timeline, including part-time study and delays in completing the research and dissertation. To discourage procrastination, universities often establish guidelines such as requiring the completion of core courses during the first year. There's also usually a maximum limit for completing all degree requirements, such as 10 years.