In non-rhotic varieties, speakers no longer pronounce /r/ in postvocalic environments—that is, when it is immediately after a vowel and not followed by another vowel. For example, a rhotic English speaker pronounces the words hard and butter as /ˈhɑːrd/ and /ˈbʌtər/, whereas a non-rhotic speaker "drops" or "deletes" the /r/ sound, pronouncing them as /ˈhɑːd/ and /ˈbʌtə/. A non-rhotic speaker usually still pronounces the /r/ in the phrase "butter and jam" (the linking R), since the /r/ is followed by a vowel in this case.
Evidence from written documents suggests that loss of postvocalic /r/ began sporadically during the mid-15th century. However, these /r/-less spellings were uncommon and were restricted to private documents, especially ones written by women. In the mid-18th century, postvocalic /r/ was still pronounced in most environments, but by the 1740s to 1770s it was often deleted entirely, especially after low vowels. By the 1790s, fully non-rhotic pronunciation had become common in London and surrounding areas, and was being increasingly used even in more formal and educated speech. By the early 19th century, the southern British standard was fully transformed into a non-rhotic variety, though some variation persisted as late as the 1870s. This loss of postvocalic /r/ in British English influenced southern and eastern American port cities with close connections to Britain, causing their upper-class pronunciation to become non-rhotic while the rest of the United States remained rhotic. Non-rhotic pronunciation continued to influence American prestige speech until the 1860s, when the American Civil War began to shift America's centers of wealth and political power to rhotic areas with fewer cultural connections to the old colonial and British elites. The advent of radio and television in the 20th century established a national standard of American pronunciation that preserves historical /r/, with rhotic speech in particular becoming prestigious in the United States rapidly after the Second World War.
The earliest traces of a loss of /r/ in English appear in the early 15th century and occur before coronal consonants, especially /s/, giving modern "ass (buttocks)" (Old English ears, Middle English ers or ars), and "bass (fish)" (OE bærs, ME bars). A second phase of /r/-loss began during the 15th century, and was characterized by sporadic and lexically variable deletion, such as monyng "morning" and cadenall "cardinal". These /r/-less spellings appear throughout the 16th and 17th centuries, but are uncommon and are restricted to private documents, especially ones written by women. No English authorities describe loss of /r/ in the standard language prior to the mid-18th century, and many do not fully accept it until the 1790s.
During the mid-17th century, a number of sources describe /r/ as being weakened but still present. The English playwright Ben Jonson's English Grammar, published posthumously in 1640, records that /r/ was "sounded firme in the beginning of words, and more liquid in the middle, and ends." Little more is said regarding /r/ until 1740, when one Mather Flint, writing in a primer for French learners of English, said: "...dans plusieurs mots, l’r devant une consonne est fort adouci, presque muet & rend un peu longue la voyale qui le precede" ("...in many words r before a consonant is greatly softened, almost mute, and slightly lengthens the preceding vowel"). By the 1770s, postvocalic /r/-less pronunciation was becoming common around London even in more formal, educated speech. The English actor and linguist John Walker uses the spelling ar to indicate the long vowel of aunt in his 1775 rhyming dictionary. In his influential Critical Pronouncing Dictionary and Expositor of the English Language (1791), Walker reported, with a strong tone of disapproval, that "... the r in lard, bard, is pronounced so much in the throat as to be little more than the middle or Italian a, lengthened into baa, baad...." Americans returning to England after the end of the American Revolutionary War in 1783 reported surprise at the significant changes in fashionable pronunciation. By the early 19th century, the southern British standard was fully transformed into a non-rhotic variety, though it continued to be variable as late as the 1870s.
The adoption of postvocalic /r/-less pronunciation as the British prestige standard in the late 18th and early 19th centuries influenced American port cities with close connections to Britain, causing upper-class pronunciation in many eastern and southern port cities such as New York City, Boston, Alexandria, Charleston, and Savannah to become non-rhotic. Like regional dialects in England, the accents of other areas in America remained rhotic in a display of linguistic "lag" that preserved the original pronunciation of /r/. Non-rhotic pronunciation continued to influence American prestige speech until the 1860s, when the American Civil War shifted America's centers of wealth and political power to areas with fewer cultural connections to the British elite. This largely removed the prestige associated with non-rhotic pronunciation in America, such that when the advent of radio and television in the 20th century established a national standard of American pronunciation, it became a rhotic variety that preserves historical /r/.