Doctor of PhilosophyDoctor of Philosophy (Ph.D., an abbreviation for the Latin "Philosophić Doctor", or D.Phil.) was originally a degree granted by a university to a learned individual who had achieved the approval of his peers and who had demonstrated a long and productive career in a learned field. The appellation of "Doctor" (from Latin: teacher) was usually awarded only when the individual was in middle age. It indicated a life dedicated to learning, to knowledge, and to the spread of knowledge.
Nowadays, the title Ph.D. is granted to a scientist or scholar who has undertaken original research in the sciences or humanities. (In the U.S there are often special divisions of universities, called graduate schools, which issue these degrees; in Australia, there is normally no division between undergraduate and postgraduate parts of the university.) Some ability to carry out original research has to be documented by producing a dissertation or thesis. In some countries the thesis must be given an oral defense, known in the UK as a viva (short for viva voce, Latin for "live voice") before a committee. The degree is often a prerequisite for permanent employment as a university professor or as a researcher in some sciences, though this varies on a regional basis. In others such as engineering or geology, a doctoral degree is considered desirable but not essential for employment.
A doctoral candidate is typically educated by a thesis advisor, or supervisor, who chairs a thesis committee which supervises the doctoral candidate. In the US, doctoral programs typically require a series of required and optional courses at the beginning of the program, but education in the latter portion of the program tends to consist of informal discussions with the thesis advisor and individual research by the student. Many universities separate the program into two portions with a required doctoral examination before allowing a student to be formally admitted to a doctoral program. The funding of students varies from field to field, and many graduate students in the sciences and engineering work as teaching assistants or research assistants while they are a doctoral student.
It typically takes several years of full time work to complete a doctoral program. In some fields such as physics, a doctoral degree is essential for employment. In some sciences, a newly graduated doctoral student is unlikely to find work as a tenure track professor and must undertake one or several postdoc positions.
In several countries (U.S, Australia) most postgraduate students doing research in this level complete a Ph.D. degree, no matter what subject area they are doing research in. In other countries, these degrees are distinguished by subject area ("Doctor of Natural Sciences", "Doctor of Social Sciences", "Dr. med."). (However, even in the U.S., there are sometimes separate degrees, e.g. Th.D. for theology, J.D for law). In some countries, the corresponding degree is simply called "Doctor". Johns Hopkins University was the first university in the United States to confer doctoral degrees.
PhDs are distinguishable from higher doctorates (such as D.Litt (Doctor of Letters) or D.Sc (Doctor of Science)), which are issued by a committee on the basis of a long record of research and publication.
Sometimes a university grants an honorary PhD called honoris causa (Latin for caused by honor), or Dr. h. c., but more commonly higher doctorates are used for this purpose.