In many accents of English, when a word ending in a vowel is followed by another vowel, a consonant R is inserted between them. This is called a linking R or epenthetic R.

I need to use SAMPA phonetic symbols in this write-up (with proper IPA [æ], [ð], [θ]), though I'll also give the examples in normal spelling. The linkage doesn't happen after all vowels. It happens after those that are to some degree open (low), or in the case of diphthongs, to those whose final segment is open. Specifically, linking [r] occurs after:

  • [@] as in ["bat@] butter, ["tSaIn@] china
  • [3:] as in [f3:] fur, [h3:] her
  • [a:] as in [ka:] car, [ma:] Ma
  • [E:] as in [fE:] fair, [ðE:] there
  • [O:] as in [pO:] poor, paw, pore, [SO:] shore, sure, Shaw
  • [I@] as in [fI@] fear, [aI"dI@] idea
  • [U@] as in [dU@] dour, [tU@] tour

Accents that do this consistently in all the above positions are the non-rhotic accents of English, those that have lost a historical [r] in final position ([ka:] car), and before a consonant ([ka:d] card). That is, original [r] was only retained when a vowel followed ([kærI] carry). These are the accents of England (except some rural), Wales, Australia, New Zealand, and South Africa, and some on the east coast of the USA.

In the remainder, the rhotic accents, most of the above example words already end in [r], so there is no linking. But some words ending in [@] (china, idea) and [O:] (or its local equivalent, in paw, Shaw) might still show the linking R effect.

The linking R occurs when a following vowel appears. This preserved the consonant in carry, and reintroduces it in [ka:r æd] car ad. Thus the R sound also appears in ["tsaIn@r @n dZ@"pæn] China and Japan, [h3:r oUn] her own, [ma:r @n pa:] Ma and Pa, etc.

It also appears in inflection. [fE:] fair becomes [fE:r@] fairer and [InSO:] insure [InSO:rIN] insuring.

It always happens in inflection, where you can't pause between morphemes, but it is possible to put a hiatus between separate words: in careful speech China and Japan might be ["tSaIn@ @nd dZ@"pæn] or even ["tSaIn@ ?@nd dZ@"pæn] with a glottal stop [?] to emphasize the break.

This is particularly likely in some speakers who distinguish between etymological and unetymological R: that is, those words like poor, fear, boring that originally had an [r] and preserve it in the spelling, and those like paw, idea, drawing that did not have one. They try to use linking R only where etymologically valid, though I say 'try to' because it is probably only in careful speech that they succeed. Nevertheless, the spread of linking R to the paw, idea type is a historical process, and had not yet spread to many speakers of Received Pronunciation (RP) in the earlier twentieth century. Some people who make this distinction regard the universal use as 'incorrect', and the effect may be called 'intrusive R' in these circumstances.

All speakers of rhotic accents also face this choice in phrases such as the idea of it. Excalibre tells me in General American they just use a hiatus, or glottal stop for emphasis, not [r]; I don't know any details for other rhotic accents, except that the Bristol variety of South-West England has the unusual Bristol L here.

I have used modern RP pronunciations as examples but the principle applies in the same way to all the non-rhotic accents. Note that for some speakers of non-rhotic accents, some of my example words are pronounced differently (sure, poor rhyme with tour, or conversely tour rhymes with shore, and fear is two syllables). There may also be triphthongs [aI@] ire and [aU@] our, hour. None of these affect the principle.

The two long vowels [E:] air, heir and [O:] ore, awe are often diphthongs [E@] and [O@], especially at the ends of words. In this case all the affected vowels but [a:] are, ah end in schwa. So [r] acts like a 'glide' (a not very precise phonetic term). corresponding to the consonants [j] of you and [w] of woo, which may occur after close (high) vowels when followed by another vowel. So the following are (almost exactly) parallel:

  • [tu:] two, [tu:w @v @ kaInd] two of a kind
  • [θri:] three, [θri:j @v @ kaInd] three of a kind
  • [fO:] four, [fO:r @v @ kaInd] four of a kind
The three other open vowels, [æ] as in hat, [a] as in hut, and [Q] as in hot, can't occur word-finally, so the effect doesn't apply to them. However, the local London accents such as Cockney do allow [æ] at the end of a word, as in [næ:] now. This also takes linking R: [nær @n den] now and then. In standard English this word has a diphthong, so [næU] takes the w-glide instead, [næUw @n ðen].

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