The degree was revived in the 19th century at the Humboldt University as a degree to be granted to someone who had undertaken original research in the sciences or humanities. From here it spread to the US, arriving in the UK at the start of the 20th century. This displaced the existing Doctor of Philosophy degree in some Universities - for instance the D.Phil (higher doctorate in the faculty of philosophy) at the University of St Andrews was discontinued an replaced with the Ph.D. (research doctorate).
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 at this level complete a Ph.D. degree, regardless of the subject area, though there are many other doctoral degrees with different designations, e.g. D.A (Doctor of Arts), D.M.A (Doctor of Musical Arts), Ed.D (Doctor of Education), Th.D. (Doctor of Theology), etc. In some countries, the corresponding degree is simply called "Doctor" or else is distinguished by subject area ("Doctor of Natural Sciences", "Doctor of Social Sciences", "Dr. med."). Johns Hopkins University was the first university in the United States to confer doctoral degrees. In the United Kingdom, Ph.D.s 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. In Switzerland the European Graduate School has a Dr.Phil on Communication.
While the Ph.D. is the most common doctoral degree, and even often (mis)understood to be synonymous with the term “doctorate,” the U.S. Department of Education and the U.S. National Science Foundation (NSF) recognize numerous doctoral degrees as equivalent, and do not discriminate between them.
The Ph.D. is often the topic of scholarly debate and criticism, given its almost exclusive concern with research and publication to the alleged neglect of numerous other faculty responsibilities that include teaching, collegial evaluation, collective and individual curricular planning, etc. Solutions have met with varying degrees of success. In the 1960s, the prestigious Carnegie Foundation helped promote and establish the Doctor of Arts degree as an alternative to the Ph.D. The D.A. degree, with its focus on content specialty, curriculum design, and pedagogy, was designed to help prepare expert teachers in various fields. Its well-defined disciplinary focus makes it different than the Ed.D (Doctor of Education) while still embracing the Ed.D.'s concern for issues in education. The D.A. continues to be offered in many universities across the United States and in other countries, but, like many innovations, including the Ed.D., faces frequent bias. A few D.A. programs have since been converted to the Ph.D. model. (Still, the D.A. has many steadfast supporters.) Other solutions include a re-thinking of the Ph.D. in order to address its perceived shortcomings.
Sometimes a university grants an honorary Ph.D. or D.A., or other doctoral degree, with the added designation of honoris causa (Latin for caused by honor), or Dr.h.c.