Linking R and intrusive R are sandhi or linking phenomena involving the appearance of the rhotic consonant (which normally corresponds to the letter ⟨r⟩) between two consecutive morphemes where it would not normally be pronounced. These phenomena occur in many non-rhotic varieties of English, such as those in most of England and Wales, part of the United States, and all of the Anglophone societies of the southern hemisphere, with the exception of South Africa. These phenomena first appeared in English sometime after the year 1700.
By definition, non-rhotic varieties of English only pronounce /r/ when it immediately precedes a vowel. This is called r-vocalisation, r-loss, r-deletion, r-dropping, r-lessness, or non-rhoticity.
For example, in non-rhotic varieties of English, the sound /r/ does not occur in a word such as tuner when it is spoken in isolation, before an intonation break (in pausa), or before a word beginning with a consonant. Even though the word is spelled with an ⟨r⟩ (which reflects that an /r/ was pronounced in the past), non-rhotic accents do not pronounce an /r/ when there is no vowel sound to follow it. Thus, in isolation, speakers of non-rhotic accents may pronounce the words tuner and tuna identically as /ˈtjuːnə/ (or /ˈtuːnə/ with the yod-dropping that typically occurs in the non-rhotic dialects of the northeastern United States, or /ˈtʃuːnə/ with the yod-coalescence that occurs in Southern Hemisphere English).
In contrast, speakers of rhotic dialects, such as those of Scotland, Ireland, and most of North America (except in some of the Northeastern United States and Southern United States), always pronounce an /r/ in tuner and never in tuna so that the two always sound distinct, even when pronounced in isolation. Hints of non-rhoticity go back as early as the 15th century, and the feature was common (at least in London) by the early 18th century.
In many non-rhotic accents, words historically ending in /r/ (as evidenced by an ⟨r⟩ in the spelling) may be pronounced with [r] when they are closely followed by another morpheme beginning with a vowel sound. So tuner amp may be pronounced [ˈtjuːnər æmp].[nb 1] This is the case in such accents even though tuner would not otherwise be pronounced with an [r]. Here, "closely" means the following word must be in the same prosodic unit (that is, not separated by a pausa). This phenomenon is known as linking R. Not all non-rhotic varieties feature linking R. A notable non-rhotic accent that does not have linking R is Southern American English.
The phenomenon of intrusive R is an overgeneralizing reinterpretation of linking R into an r-insertion rule that affects any word that ends in the non-high vowels /ə/, /ɪə/, /ɑː/, or /ɔː/; when such a word is closely followed by another word beginning in a vowel sound, an [r] is inserted between them, even when no final /r/ was historically present. For example, the phrase bacteria in it would be pronounced /bækˈtɪəriərˌɪnɪt/. The epenthetic [r] can be inserted to prevent hiatus, two consecutive vowel sounds.
Other recognizable examples are the Beatles singing: "I saw-r-a film today, oh boy" in the song "A Day in the Life", from their 1967 Sgt. Pepper's Lonely Hearts Club Band album, in the song "Champagne Supernova" by Oasis: "supernova-r-in the sky", at the Sanctus in the Catholic Mass: "Hosanna-r-in the highest" and in the phrases, "Law-r-and order" and "Victoria-r-and Albert Museum". This is now common enough in parts of England that, by 1997, the linguist John C. Wells considered it objectively part of Received Pronunciation, though he noted that it was still stigmatized as an incorrect pronunciation, as it is or was in some other standardized non-rhotic accents. Wells writes that at least in RP, "linking /r/ and intrusive /r/ are distinct only historically and orthographically".
Rhotic dialects do not feature intrusive R. A rhotic speaker may use alternative strategies to prevent the hiatus, such as the insertion of a glottal stop to clarify the boundary between the two words. Varieties that feature linking R but not intrusive R (that is, tuna oil is pronounced [ˈtjuːnə (ʔ)ɔɪl]), show a clear phonemic distinction between words with and without /r/ in the syllable coda.
Some speakers intrude an R at the end of a word even when there is no vowel following. An example is U.S. President George W. Bush (who is from Texas) speaking to Federal Emergency Management Agency director Michael Brown in 2005: "The FEMA-R director's working 24/7".
A study examined the pronunciation of 30 British newsreaders on nationally broadcast newscasts around the turn of the 21st century speaking what was judged to be "mainstream RP". The data used in the study consisted mostly of the newsreaders reading from prepared scripts, but also included some more informal interview segments. It was found that all the newsreaders used some linking R and 90% (27 of 30) used some intrusive R.
Overall, linking R was used in 59.8% of possible sites and intrusive R was used in 32.6% of possible sites. The factors influencing the use of both linking and intrusive R were found to be the same. Factors favouring the use of R-sandhi included adjacency to short words; adjacency to grammatical or non-lexical words; and informal style (interview rather than a prepared script). Factors disfavouring the use of R-sandhi included adjacency to proper names; occurrence immediately before a stressed syllable; the presence of another /r/ in the vicinity; and more formal style (prepared script rather than interview). The following factors were proposed as accounting for the difference between the frequency of linking and intrusive R: