Doctor of Philosophy, abbreviated as Ph.D., PhD, D.Phil., or DPhil (for the Latin philosophiae doctor or doctor philosophiae), in English-speaking countries, is a postgraduate academic degree awarded by universities. The academic level of degrees known as doctorates of philosophy varies considerably according to the country, institution, and time period, from entry-level research degrees to higher doctorates.
The term "philosophy" does not refer solely to the modern field of philosophy, but is used in a broader sense in accordance with its original Greek meaning, which is "love of wisdom". In most of Europe, all fields other than theology, law and medicine were traditionally known as philosophy.
The doctorate of philosophy as it exists today originated as a doctorate in the liberal arts at the Humboldt University, and was eventually adopted by American universities, becoming common in large parts of the world in the 20th century. In many countries, the doctorate of philosophy is still awarded only in the liberal arts (known as "philosophy" in continental Europe, hence the name of the degree).
In the United States, the Ph.D. degree is the highest academic degree awarded by universities in most fields of study. American students typically undergo a series of three phases in the course of their work toward the Ph.D. degree. 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, a comprehensive examination, or a series of cumulative examinations where the emphasis is on breadth rather than depth of knowledge. The student is often later required to pass oral and written examinations in the field of specialization within the discipline, and here, depth is emphasized. Some Ph.D. programs require the candidate to successfully complete requirements in pedagogy (taking courses on higher level teaching and teaching undergraduate courses) or applied science (e.g., clinical practice 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 typically ranges from 50 to 450 pages in length. In many cases, depending on the discipline, a dissertation consists 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. degree is often a preliminary step toward a career as a professor, throughout the whole period of study and dissertation research the student, depending on the university and degree, may be required or offered the opportunity to teach undergraduate and occasionally graduate courses in relevant subjects.
Admission
There are 282 universities in the United States that award the PhD degree, and those universities vary widely in their criteria for admission, as well as the rigor of their academic programs. Typically, PhD programs require applicants to have a Bachelor's degree in a relevant field (and, in many cases in the humanities, a master's degree), reasonably high grades, several letters of recommendation, relevant academic coursework, a cogent statement of interest in the field of study, and satisfactory performance on a graduate-level exam specified by the respective program (e.g., GRE, GMAT). Specific admissions criteria differ substantially according to university admissions policies and fields of study. Some programs in well-regarded research universities may have very low acceptance rates and require excellent performances on the GRE and in undergraduate work, strong support in letters of recommendation, substantial research experience, and academically sophisticated samples of their writing.
Master's degree "en route"
As applicants to many Ph.D. programs are not required to have master's degrees, many programs award a Master of Arts or Master of Science degree "en route", "in passing", or "in course" based on the graduate work done in the course of achieving the Ph.D. Students who receive such master's degrees are usually required to complete a certain amount of coursework and a master's thesis or field examination. Not all Ph.D. programs require additional work to obtain a master's en route to the Ph.D. (e.g., a master's thesis). Depending on the specific program, masters-in-passing degrees can be either mandatory or optional. Not all Ph.D. students choose to complete the additional requirements necessary for the MA or MS if such requirements are not mandated by their programs. Those students will simply obtain the Ph.D. degree at the end of their graduate study.
Time
Depending on the specific field of study, completion of a PhD program usually takes four to eight years of study after the Bachelor's Degree; those students who begin a PhD program with a master's degree may complete their PhD degree a year or two sooner. As PhD programs typically lack the formal structure of undergraduate education, there are significant individual differences in the time taken to complete the degree. Many U.S. universities have set a ten-year limit for students in PhD programs, or refuse to consider graduate credit older than ten years as counting towards a PhD degree. Similarly, students may be required to re-take the comprehensive exam if they do not defend their dissertations within five years after submitting it to their self-chosen dissertation advisors. Overall, 57% of students who begin a PhD program in the US will complete their degree within ten years, approximately 30% will drop out or be dismissed, and the remaining 13% of students will continue on past ten years.
Funding
PhD students are usually discouraged from engaging in external employment during the course of their graduate training. As a result, PhD students at U.S. universities typically receive a tuition waiver and some form of annual stipend. The source and amount of funding varies from field to field and university to university. Many U.S. PhD students work as teaching assistants or research assistants. Graduate schools increasingly encourage their students to seek outside funding; many are supported by fellowships they obtain for themselves or by their advisers' research grants from government agencies such as the National Science Foundation and the National Institutes of Health. Many Ivy League and other well-endowed universities provide funding for the entire duration of the degree program (if it is short) or for most of it.
PhD candidacy
A PhD program candidate, or PhDc (sometimes called Candidate of Philosophy), is a postgraduate student at the doctoral level who has successfully satisfied the requirements for doctoral studies, except for the final thesis or dissertation. As such, a PhDc is sometimes called an "ABD" (All But Dissertation or All But Defended). Although a minor distinction in postgraduate study, achieving PhD Candidacy is not without benefit. For example, PhDc status may coincide with an increase in the student's monthly stipend and may make the student eligible for additional employment opportunities.
Some programs also include a Master of Philosophy degree as part of the PhD program. The MPhil, in those universities that offer it, is usually awarded after the appropriate MA or MS (as above) is awarded, and the degree candidate has completed all further requirements for the PhD degree (which may include additional language requirements, course credits, teaching experiences, and comprehensive exams) aside from the writing and defense of the dissertation itself. This formalizes the "all but dissertation" (ABD) status used informally by some students, and represents that the student has achieved a higher level of scholarship than the MA/MS would indicate – as such, the MPhil is sometimes a helpful credential for those applying for teaching or research posts while completing their dissertation work for the PhD degree itself.
PhDc is not to be confused with Candidate of Sciences, an academic degree that has been used in certain countries in place of PhD.