I have heard many people say they have a PhD in a certain area. For nearly all of my life, I thought a PhD was simply a doctorate, and I didn't know that it had anything to do with philosophy.

There are many doctoral degrees, why are PhD's the most popular doctoral degrees by a long shot?

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    "There are many doctoral degrees" ... To clarify the question, can you provide examples of these other types of degrees that are common in your area? Commented Dec 28, 2017 at 21:12

5 Answers 5


This answer suffered a Major Revision!

A Ph.D. is an academic doctoral degree and have nothing to do with philosophy nowadays.

From Wikipedia:

In the context of the Doctor of Philosophy and other similarly titled degrees, the term "philosophy" does not refer to the field or academic discipline of philosophy, but is used in a broader sense in accordance with its original Greek meaning, which is "love of wisdom".

People often refers to an academic doctorate as a Ph.D., even when the official title in their university/country is different of Doctor of Philosophy. The reason beyond its popularity is because a Ph.D. is a title traditionally conceded in countries with anglo-saxonic language and since the common language in the academia is English we often "translate" our titles to the equivalent in English.

I have recently learned with @Pete L. Clark that there are different types of doctorates in the US that give the same legal statute as an academic doctorate, but with different structure and requisites from a doctorate in Science. The example that he used was the Doctor of Arts (D.A.), a title that gives equivalent rights as a Ph.D. in which concerns teaching and research in universities.

My previous misunderstanding was due to the structure of high level education that I am used to in Portugal and Brazil. In both countries Therapists, Physicians, Lawyers and others do not have a doctoral degree. In Portugal a physician have Master's degree in Health Science or a 6 years pre-bologna licenciatura degree (undergraduate degree). If a physician/lawyer/therapists wants to have a doctoral degree here they need to engage in a minimum 3 years doctoral course, publish articles and defend an original thesis.

For a historical insight and more complete overview, please read this article and this article.

I'm sorry for the previous wrong answer. I think the question is too wide and depends highly on which country we are talking about. I assumed things about the doctoral degrees on the US that are not true.

Edit: Of course that there are many different ways to refer to an academic doctorate depending on the country the title is emitted. The point is: they are all equivalent. A German Doktorgrad is equivalent to a Ph.D. in the UK and to a Doutoramento/Doutorado in Portugal/Brazil, etc. In the other way researchers would not be able to work across the borders.

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    This seems untrue, ish. In common communication, yes, a doctorate refers to a PhD, but hearing it applied to MD is not uncommon. And technically, various other doctorates exist: JD (lawyer), DMD (dentist), DSD (dental surgeon), OD (optometrist), DVM (vet), PsyD (psychologist, though it’s relatively new and a PhD in psychology is the more common doctorate in that field), etc. The thrust of the question, I think, is why so many fields congregate under PhD instead of each having their own _D, like some of the above.
    – KRyan
    Commented Dec 27, 2017 at 5:03
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    This answer is unfortunately wrong: Even Wikipedia states in the first paragraph of its "Doctorate" article that "There are a variety of doctoral degrees, with the most common being the Doctor of Philosophy (PhD), which is awarded in many different fields, ranging from the humanities to the scientific disciplines". There are MDs, D.Phil, D.Eng, German-style D. rer. nat. etc. Commented Dec 27, 2017 at 15:43
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    @TheDoctor No, you are again wrong. Just because "doctor" in English sounds like "Doutorado" in Portuguese does not mean they are interchangeable: Holders of a Doutorado are doctors but not all doctors hold a Doutorado. Moreover, this has nothing to do with countries: The UK has PhDs, D.Phils, D.Eng, which are all doctorates but are not equivalent. I'm now downvoting because you don't seem to understand the differences and are strongly arguing that there are none, which is dangerous to others. Commented Dec 27, 2017 at 16:11
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    @TheDoctor The difference is that you can get a D.Phil from Oxford but not a PhD. Stop looking for low-hanging fruit: See the Doctor of Engineering degree, which is not even functionally equivalent like D.Phil and PhD are. Commented Dec 27, 2017 at 16:19
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    @errantlinguist Giving you the benefit of the doubt that you're genuinely asking: Your overall rhetoric is ineffective here because it reeks of elitism and dismissive bias, with just a hint of sycophantic melodrama. Pete's references clearly support the validity of his claims with concrete examples, while the purpose and applicability of your reference is unclear and gives an incoherent impression of frustratedly grasping for an emotionally appealing but ultimately flimsy argument. At least, those appear to be the main differences...
    – MickLH
    Commented Dec 28, 2017 at 0:23

PhDs are more common because PhDs come from all fields and most countries. To talk in broad strokes (I suggest looking into each of these points, e.g. in wikipedia for more details.)

Lets break our doctorates into 3 kinds:

Research Doctorates

These are given for doing research, and intended to train researchers.

  • Doctorate of Philosophy (PhD)
    • all fields of study, in all countries
  • Doctorate of ___ field

Higher doctorates

  • Doctor of Letters (Arts, Humanitites), Doctor of Science etc

    • Field specific doctorate
    • more or less lifetime achievement awards for research.
    • Generally pre-req'd on having a PhD for at least 10 years.
  • Dr. habil

    • see Habilitation
    • Most common (but not restricted to) in Germany, Austria, Swizerland.
    • Requires a PhD equivalent

Obviously there will be less people with any given higher doctorate than PhDs since they are a subset of people who have PhDs with in a given field.

Professional Doctorates

These are doctoral degrees that are required to do a profession.

  • Medicine Doctor (MD) i.e. a Doctor of Medicine
    • Every "doctor" in a hospital has at least this.
  • Juris Doctor (JD) i,e Doctor of Jurisprudence
    • which in many countries required to be a lawyer
    • by tradition laywers never take the title Dr.

There are a lot of professional doctorate holders. You've probably seen the thing about PhD holders not using the title Dr on plane tickets because they don't want to be called upon for medical assistance (which they can not provide).

There are probably more PhDs awarded each year than MDs. But not by a huge margin.

In 2014 the US had 18,078 MDs graduate (source) and 54,070 PhDs; of those only about 40,000 were in science and engineering and of those only a very small portion would be in medical science (source).

Also in 2014 the US had 43,832 JDs graduate (source). This is as compared to only 14,000 nonscience and engineering PhDs; of which only a small portion of which would be in Law.

I posit that for any field with a professional doctorate (I can only think of MD and JD) there will be an order of magnitude more professional doctorates than PhDs in that field.

The only reason PhD numbers are so high vs professional doctorates, is because they are the same degree no matter the field.

Similarly, the only reason they are high compared to Dr.Ing etc is that those degree are only common in certain countries; and are field specific.

And vs Higher doctorates: they are prerequed on PhD, and are field specific.

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    PhDs do not exist in "all countries" as you listed. In fact, this is contradicted by your next item where "some countries" in fact award "doctorates of [xxx]". For example, I don't really have a "PhD", I have a "doctorat de mathématiques". It's simply easier to say that I have a PhD to English-speaking people. Regarding habilitation, it's not "Germany, Austria, Switzerland and a few other countries". According to Wikipedia, it's at least 28 countries that I'm not going to list. Habilitation is also not a "higher doctorate", by the way. This answer is full of approximations (not to say errors).
    – user9646
    Commented Dec 27, 2017 at 8:58
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    Note also that in some countries PhDs (or doctorates) were introduced in relatively recent times. For instance, in my country, Italy, this degree was introduced only 34 years ago. Commented Dec 27, 2017 at 9:34
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    Getting a PhD typically requires a bachelor degree (or equivalent), and yet nobody thinks of a PhD as a "higher bachelor". Habilitation is a qualification that says "you are fit to direct a research group" (incl PhD students, postdocs...).
    – user9646
    Commented Dec 27, 2017 at 13:17
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    I have a French "doctorat en informatique", which was found to be equivalent to a PhD in the Canadian system... A rose called by another name and all that... Commented Dec 27, 2017 at 15:05
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    The doctorate-vs.-habilitation issue is further confused by the circumstance that at one time (perhaps still now but I don't have recent information), the Russian (at that time Soviet) system had two degrees of this sort. One, equivalent to a doctorate in the U.S. or Germany, had a name that sounded like "candidate". The other, equivalent to a German habilitation, had a name that sounded like "doctor". Commented Dec 27, 2017 at 17:35

In one's early education, especially in more traditional contexts, learning involved X being true because the teacher said so. Don't question the teacher; just make sure that you know X. It was all about memorization (rote learning).

This would start to change when a student would reach the highest levels of education, at which point they'd be able to argue and contribute their own understanding. So instead of focusing on rote learning, a student would have to demonstrate their ability to think and engage in critique of their field (scholasticism). This is, successful students would become philosophers of their field rather than simple repositories of memorized facts.

Education's become increasingly liberal with a shift from rote learning toward critical thinking, but there's still a semblance of that early expectation that pre-Ph.D. students are supposed to memorize what's being taught while a Ph.D. would symbolize one's ability to go beyond that.

Historical background

Academics used to be folks who participated in medieval universities. There was a heavy religious flavoring to academia compared to today's more secular settings, but it was still general academia nonetheless.

A lot of stuff came from this time. For example, on graduation when you dress up like Harry Potter, it's because that's how these guys used to dress.

Anyway, so this is where the Bachelor's/Master's/doctorate thing came from:

Course of study

University studies took six years for a Master of Arts degree (a Bachelor of Arts degree was awarded after completing the third or fourth year). Studies for this were organized by the faculty of arts, where the seven liberal arts were taught: arithmetic, geometry, astronomy, music theory, grammar, logic, and rhetoric. All instruction was given in Latin and students were expected to converse in that language. The trivium comprised the three subjects that were taught first: grammar, logic, and rhetoric. These three subjects were the most important of the seven liberal arts for medieval students. The curriculum came also to include the three Aristotelian philosophies: physics, metaphysics and moral philosophy.

-"Medieval university", Wikpiedia [links and citations omitted]

And that stuff was a lot of the rote learning, before one was a proper doctor.

After that, one'd go into the realm of philosophy, becoming a more critical thinker (scholar):

Once a Master of Arts degree had been conferred, the student could leave the university or pursue further studies in one of the higher faculties, law, medicine, or theology, the last one being the most prestigious. A popular textbook for theological study was called the Sentences (Quattuor libri sententiarum) of Peter Lombard; theology students as well as masters were required to write extensive commentaries on this text as part of their curriculum.[citation needed] Studies in the higher faculties could take up to twelve years for a master's degree or doctorate (initially the two were synonymous), though again a bachelor's and a licentiate's degree could be awarded along the way.

-"Medieval university", Wikpiedia [links and citations omitted]

This system was already established by the time "science" started to be recognized in a more modern sense. At that time, it was still just Philosophy, or more specifically "Natural Philosophy".

So, to be a "doctor of philosophy" is literally just that - to be a scholar of philosophy who's gone beyond the intro years of rote memorization to the point where they can engage in scholarly critique of their field.

Ph.D.'s as further Master's degrees

In the historical context in which these degrees were named, the human knowledge pool was way, way smaller. It was a drop compared to today's oceans. And so, the prospect of learning much of the human knowledge pool was far more reasonable, if many'd still have regarded it as challenging.

Today, a lot of Ph.D.'s are awarded to students who probably don't quite get the whole philosophy-of-their-field thing. That seems to be a natural consequence of there being a lot more one can learn before reaching the point of critique and abstraction.

So, today, a Ph.D. can be something like a fancy Master's degree. For example, one can basically get a Master's in Chemistry, then do a bunch of lab work to test something out, and get a Ph.D. for that (experimental chemistry).

In principle, we might argue that there's some need for revision to the academic credentialing system to better capture its modern reality. And we've actually kinda done that already - as noted in the Wikipedia link above, a Master's and doctorate used to be the same thing; they got more separated in part due to the human knowledge pool growing and more ranks being needed to account for it. But that'd be a different topic.

For the purposes of this question, a Ph.D. got its name in the scholarly days when academics were basically those who learned their field and then engaged in scholarly critique of it. And today, the name's kinda a historical artifact.

Further reading

I found a neat paper that discusses the evolution of doctoral conference since the scholarly days:

This document's a look at what scholastics/academics had to do to be recognized as a doctor. And while the title specifies "On Dissertations", it notes:

Less than a century ago a dissertation was not always required to obtain a doctorate. Successfully defending a number of theses sufficed. [-page 7]

Other interesting factoids:

  • Apparently dissertations used to be more about disputing (critique) points, written up as a disputation. This contrasts with the modern description of a PhD being about adding to the human knowledge pool.

  • It seems like prior academia was far more concerned with religion than modern academia. Early academics seem to have been something like clergy.

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    I don't see how this answers the question, he is asking why are phd popular degrees among other doctoral degrees. Commented Dec 27, 2017 at 10:59
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    @HermanToothroth Was primarily responding to the "For nearly all of my life, i thought a phd was simply a doctorate, and i didn't know that it had anything to do with philosophy." part by explaining the connection between a PhD and Philosophy. Ultimately it's just a name that had historical grounding. After its historical inception, the name's just stuck around.
    – Nat
    Commented Dec 27, 2017 at 11:13
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    @HermanToothroth If I understand correctly, to put it another way, this answer is saying that PhD's are the most common doctoral degrees simply because "PhD" was the term most commonly chosen for degrees at that level. And it also gives a justification for why the designation "PhD" was chosen so often, at least in older times.
    – David Z
    Commented Dec 27, 2017 at 11:50
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    This answer is actually wrong: PhDs originally did not entail original research at all, just lengthy scholarship and examination. The title comes literally from the meaning of philosophia-- love of wisdom. You were a doctor of philosophia because back then there was no distinction between e.g. biology, mathematics, astronomy... If you were smart and we're good at it, you could work in the field. Even today, e.g. physics PhDs can and do work in e.g. computer science. Commented Dec 27, 2017 at 13:05
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    Not to toot my own horn, but my answer explains the historical precedent behind the name philosophiae doctor from the history of philosophia. Commented Dec 27, 2017 at 15:45

The title philosophiae doctor is a remnant from a time when there were no "degree requirements" for jobs and there was not a myriad of different sub-fields: the title "doctor of philosophy" comes from the Greek philosophia, literally "love of wisdom". In other words, doctors of "philosophy" were originally much more "free" in what they could and did contribute to intellectually, which is more of an artifact of how far we've progressed in terms of research between now and then than anything else (cf. Wikipedia for a good overview of university structure from Medieval times onwards).

This is shown by the great number of polymaths in the past in relation to now, including but in no way limited to

  • Aristotle (384–322 BC),
  • Archimedes (c.287–c.212 BC)
  • Ptolemy (90–168 AD)
  • Jābir ibn Hayyān (Geber) (721–815)
  • Ibn Hazm al-Andalusi (994–1064)
  • Hildegard von Bingen (1098–1179)
  • Leon Battista Alberti (1404–1472)
  • Leonardo da Vinci (1452–1519)
  • Copernicus (1473–1543)
  • Matrakçı Nasuh (1480–c.1564)
  • Akbar the Great (1542–1605)
  • Isaac Newton (1643–1727)
  • Gottfried Leibniz (1646–1716)
  • Benjamin Franklin (1706–1790)
  • Mikhail Lomonosov (1711–1765)
  • David Hume (1711–1776)

(cf. John Chiappone's Intro to Humanities site for many more)

There are many more people with higher degrees now per capita than there were back then, so there should theoretically be more polymaths now, but the state of the art has progressed to a level that staying cutting-edge in many fields at once is now much harder. However, even now, people who earned their PhD in one field can and often do go on to contribute to other fields, thus meaning that the spirit of the doctor philosophiae is still alive.

Xkcd made a comic of a very old joke which illustrates this well, but the joke as I know it repeats "A is just applied B" until it terminates at something like

  1. Mathematics is just applied logic, and
  2. logic is just applied philosophy.

Being someone with a philosophy-leaning background myself, I'd say the author stopped at mathematics because he's a mathematician (it turns out he's a physicist with a sense of humor good enough to be make fun of himself!).

Origins of the PhD title and its spread

The PhD title originated in Germany as a comprehensive title not specific to any field and was popularized by Americans who studied there and brought the title back to the US. See Wikipedia:

This situation changed in the early 19th century through the educational reforms in Germany, most strongly embodied in the model of the University of Berlin, founded and controlled by the Prussian government in 1810. The arts faculty, which in Germany was labelled the faculty of philosophy, started demanding contributions to research,[15] attested by a dissertation, for the award of their final degree, which was labelled Doctor of Philosophy (abbreviated as Ph.D.)—originally this was just the German equivalent of the Master of Arts degree. Whereas in the Middle Ages the arts faculty had a set curriculum, based upon the trivium and the quadrivium, by the 19th century it had come to house all the courses of study in subjects now commonly referred to as sciences and humanities.[16] Professors across the humanities and sciences focused on their advanced research.[17] Practically all the funding came from the central government, and it could be cut off if the professor was politically unacceptable.[relevant? – discuss][18]

These reforms proved extremely successful, and fairly quickly the German universities started attracting foreign students, notably from the United States. The American students would go to Germany to obtain a PhD after having studied for a bachelor's degrees at an American college. So influential was this practice that it was imported to the United States, where in 1861 Yale University started granting the PhD degree to younger students who, after having obtained the bachelor's degree, had completed a prescribed course of graduate study and successfully defended a thesis or dissertation containing original research in science or in the humanities.[19] In Germany, the name of the doctorate was adapted after the philosophy faculty started being split up − e.g. Dr. rer. nat. for doctorates in the faculty of natural sciences − but in most of the English-speaking world the name "Doctor of Philosophy" was retained for research doctorates in all disciplines.

The PhD degree and similar awards spread across Europe in the 19th and early 20th centuries. The degree was introduced in France in 1808, replacing diplomas as the highest academic degree; into Russia in 1819, when the Doktor Nauk degree, roughly equivalent to a PhD, gradually started replacing the specialist diploma, roughly equivalent to the MA, as the highest academic degree; and in Italy in 1927, when PhDs gradually started replacing the Laurea as the highest academic degree.[citation needed]

Despite specialist terminal degrees appearing in other countries, this never gained much traction in the US and to a lesser extent in other parts of the Anglosphere. Additionally, in the Anglosphere (especially in the US), the ideal of greater education as being truly comprehensive in this manner seems to remain stronger than in e.g. continental Europe, with the tradition of liberal arts still being very strong there while being relatively uncommon in higher levels of education in continental Europe. This could explain how the modern notion of the single title "PhD" as a terminal research degree seems to have spread from the US: Many universities outside the Anglosphere which previously offered terminal degrees other than the PhD are now offering them as a trend of the times and increased internationalization, thus explaining some of the perceived convergence towards the PhD as a single terminal degree even outside of the Anglosphere.

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    The author is a physicist, not a mathematician. Commented Dec 27, 2017 at 15:10
  • @DanielFischer thanks; physicist also makes a lot of sense. Commented Dec 27, 2017 at 15:27
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    This answer is pure speculation with little actual information, except a long and pointless list of "polymaths". I would need some actual evidence to believe that the fact that a PhD is the US degree for most research doctorates has something to do with the liberal arts tradition. PhD education in the US is narrowly focused and has no liberal arts element to it. Even breadth requirements in PhD programs are limited to the field of study. Commented Dec 27, 2017 at 22:04
  • @SashoNikolov I supplied a huge amount of links which you can read about; What "actual evidence" do you need if that is not enough for you? Moreover, what is your knowledge of higher education in the US? is your specialization in the history of education? Commented Dec 27, 2017 at 22:49
  • @SashoNikolov I now added explicit passages from Wikipedia illustrating the connection between philosophy, the liberal arts and the modern PhD title. On the linked Wikipedia pages you will find many bibliographic references to books which explain history much better than I can do. Commented Dec 27, 2017 at 23:32

A Ph.D. refers to an academic doctorate. Which means it is awarded upon completing a body of original research in recognition of such completion. Professional doctorate degrees -- MD, JD, DMD, DDS, DO, DC, Psy. D., Pharm.D (and I am borrowing this list from one of the other answers to this question) -- are awarded in recognition of attaining a high level of professional training in those disciplines.

Incidentally, "philosophy" used to refer to all studies which we call academic today. So the title "Philosophy Doctor" stems from those times.

BTW, there is a number of people with double titles MD,Ph.D and DDS,Ph.D. These indicate both academic research credentials and clinical training credentials. Presumably, a Ph.D. (in one of life sciences) could be received without ever seeing a human patient. Whereas an MD is more patient-oriented.

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