The primary meaning of Doctor in English has historically been with reference to the holder of a doctoral degree. These particularly referred to the ancient faculties of divinity, law and medicine, sometimes with the addition of music, which were the only doctoral degrees offered until the 19th century. During the 19th century, PhDs became increasingly common in Britain, although to obtain the degree it was necessary to travel to continental Europe or (from 1861) to the United States, as the degree was not awarded in the UK until 1917.

However, the title, not being protected by law, was adopted by. As a result, by the mid 19th century, it was normal in the UK to omit the title “Dr” when addressing letters to those holding doctoral degrees, and instead write the abbreviated form of the degree after the name, eg The Reverend Robert Phelps, DD ”, Thomas Elliotson, Esq. MD ”, or John Lindsey, Esq. Ph.D. ”, in order to avoid classing academic doctors“ with the village apothecary and the farrier ”and various“ quacks in literature, science, or art ”. In the US it similarly became customary to use post-nominals rather than the title of Doctor when addressing letters.