question: What makes the letter "R" different from all the other letters?
comment: English does indeed have [R-colored vowels]( URL_0 ), which are exactly what they sound like; you make the vowel but move your mouth towards the "r" shape, which "colors" the vowel and makes it sound like an R. This is partially because some types of consonant (in English, the R and L sounds in particular) come with "built-in" vowels that you always say as part of the consonant, but mainly it's a quirk of English. Worldwide, R-colored vowels are extremely rare. It happens that two of the most widespread languages (English and Mandarin) use them, but in most language families they're almost nonexistent. I can't speak to why they're hard to learn, though. Hope this helps!
passages: The name of the letter in Latin was (), following the pattern of other letters representing continuants, such as F, L, M, N and S. This name is preserved in French and many other languages. In Middle English, the name of the letter changed from to , following a pattern exhibited in many other words such as "farm" (compare French "ferme"), and "star" (compare German "Stern").
  
  In Hiberno-English the letter is called or , somewhat similar to "oar", "ore", "orr".
   In several European languages, such as Catalan, Spanish, Portuguese or Albanian, "rr" represents the alveolar trill (or the voiced uvular fricative in Portuguese) and contrasts with the single "r", which represents the alveolar tap (in Catalan and Spanish a single "r" also represents the alveolar trill at the beginning of words or syllables). In Italian or Finnish, "rr" is furthermore a geminate (long) consonant . In Central Alaskan Yup'ik it is used for . In Cornish, it can represent either , , or .
  
  Section::::S.
   Ŕ
  
  Ŕ (minuscule: ŕ) is a letter of the Slovak and Lower Sorbian alphabets. It is formed from R with the addition of an acute. Their Unicode codepoints are and . The PostScript names are and .
  
  Section::::Slovak.
  
  It is used in Slovak to represent the geminate syllabic r, : .
  
  Section::::Lower Sorbian.
  
  It is used in Lower Sorbian to represent the palatalised r, : .
  
  Section::::Basque.
  
  In Sabino Arana's orthography of the Basque language, "ŕ" was used for the trill consonant.
  
  However, in the standard Basque alphabet, "r" is used in syllable-final positions and "rr" between vowels.
  
  Section::::See also.
   In Oscan, S between vowels did not undergo rhotacism as it did in Latin; but it was voiced, becoming the sound . However, between vowels, the original cluster "rs" developed either to a simple "r" with lengthening on the preceding vowel, or to a long "rr" (as in Latin), and at the end of a word, original "rs" becomes "r" just as in Latin. Unlike in Latin, the s is not dropped from the consonant clusters "sm", "sn", "sl".
  
  Section::::Example of an Oscan text.
  
  Taken from the 
  
  In Latin:
  
  Section::::See also.
  
  BULLET::::- Ancient peoples of Italy
  
  Section::::Further reading.
   Section::::Use in writing systems.
  
  Section::::Use in writing systems.:English.
  
  The letter is the eighth most common letter in English and the fourth-most common consonant (after , , and ).
  
  The letter is used to form the ending "-re", which is used in certain words such as "centre" in some varieties of English spelling, such as British English. Canadian English also uses the "-re" ending, unlike American English, where the ending is usually replaced by "-er" ("center"). This does not affect pronunciation.
  
  Section::::Use in writing systems.:Other languages.
  
   represents a rhotic consonant in many languages, as shown in the table below.
   R
  
  R (named "ar/or" ) is the 18th letter of the modern English alphabet and the ISO basic Latin alphabet.
  
  Section::::History.
  
  Section::::History.:Antiquity.
  
  The original Semitic letter may have been inspired by an Egyptian hieroglyph for "tp", "head". It was used for by Semites because in their language, the word for "head" was "rêš" (also the name of the letter). It developed into Greek 'Ρ' ("rhô") and Latin R.
   The use of the above graphemes is relatively stable and universal, taking into account dialectal mergers and so on. However, in certain areas there is somewhat more variation. A typically diverse area is in the representation of sounds not present in most varieties of Romani. For example, the centralised vowel phonemes of several varieties of Vlax and Xaladitka, when they are indicated separately from the non-centralised vowels, can be represented using ə, ъ or ă. Another particularly variant area is the representation of palatalised consonants, which are absent from a number of dialects. Some variant graphemes for include tj, ty, ć, čj and t᾿. Finally, the representation of the phoneme (the reflex of the Sanskrit retroflex series), which in several dialects has been merged with , tends to vary between rr, ř and rh, and sometimes even gh, with the first two being the most frequently found variants.
   Rhotic consonant
  
  In phonetics, rhotic consonants, or "R-like" sounds, are liquid consonants that are traditionally represented orthographically by symbols derived from the Greek letter rho, including , in the Latin script and , in the Cyrillic script. They are transcribed in the International Phonetic Alphabet by upper- or lower-case variants of Roman , : , , , , , , , and .
   Other languages may use the letter in their alphabets (or Latin transliterations schemes) to represent rhotic consonants different from the alveolar trill. In Haitian Creole, it represents a sound so weak that it is often written interchangeably with , e.g. 'Kweyol' for 'Kreyol'.
   The descending diagonal stroke develops as a graphic variant in some Western Greek alphabets (writing "rho" as ), but it was not adopted in most Old Italic alphabets; most Old Italic alphabets show variants of their "rho" between a "P" and a "D" shape, but without the Western Greek descending stroke. 
  
  Indeed, the oldest known forms of the Latin alphabet itself of the 7th to 6th centuries BC, in the Duenos and the Forum inscription, still write "r" using the "P" shape of the letter.
   Corston-Oliver (1996 & 2002) discuss about the ergativity in Roviana.
  
  Todd (2000) and Ross (1988) discuss the clause structure in Roviana.
  
  Section::::Phonology and Orthography.
  
  BULLET::::- Consonants
  
  The Roviana alphabet is based on the Latin alphabet and consists of the above letters.
  
  allophones:
  
  BULLET::::- Vowels
  
  V → V: / stressed Vs
  
  V → Ṽ / _N
  
  BULLET::::- Phonotactics
  
  (C)V
  
  Diphthongs
  
  There are five diphthongs; , , , , and 
   The other main theory is that the uvular R originated within Germanic languages by the weakening of the alveolar R, which was replaced by an imitation of the alveolar R (vocalisation). Against the "French origin" theory, it is claimed that there are many signs that the uvular R existed in some German dialects long before the 17th century. 
  
  Apart from modern Europe, uvular R also exists in some Semitic languages, including certain archaic varieties of North Mesopotamian Arabic and probably Tiberian Hebrew.
  
  Section::::Voiced uvular fricative trill.
  
  Section::::Voiced uvular fricative trill.:Features.
  
  Features of the voiced uvular fricative trill:
   In premodern Shilha orthography, two extra letters were added to the alphabet to represent consonants not represented by the Standard Arabic alphabet: a "kāf" with three dots for "g", and "ṣād" with three dots for "ẓ" (dots may also be added underneath the letter). Consonants "ṛ" and "ḷ", which bear a minimal functional load, are not distinguished in the spelling from "r" and "l".
   Section::::Use in writing systems.:Other orthographies.
  
  In most European languages written in the Latin script, such as in Romance and Germanic languages, appears almost exclusively in the digraph . In French, Occitan, Catalan and Portuguese, represents or ; in Spanish, it represents . replaces for before front vowels and , since in those languages represents a fricative or affricate before front vowels. In Italian represents (where is the semivowel allophone of ).
  
  It is not considered to be part of the Cornish (Standard Written Form), Estonian, Icelandic, Irish, Latvian, Lithuanian, Polish, Serbo-Croatian, Scottish Gaelic, Slovenian, Turkish, or Welsh alphabets.
  
  Section::::Other uses.
   Saussure's insight was to align the long-vowel roots like *"dō-, *stā"- with roots like "*bher"-, rather than with roots of the *"sed"- sort. That is, treating "schwa" not as a residue of a long vowel but, like the *"r" of *"bher-/*bhor-/*bhṛ"-, an element that was present in the root in all grades, but which in full grade forms coalesced with an ordinary "e/o" root vowel to make a long vowel, with "coloring" (changed phonetics) of the "e"-grade into the bargain; the mystery element was seen by itself only in zero grade forms:
   In Livonian, whose alphabet is based on a mixture of Latvian and Estonian alphabets, the comma is used on the letters "ḑ", "ļ", "ņ", "ŗ", "ț" to indicate palatalization in the same fashion as Latvian, except that Livonian uses "ḑ" and "ț" represent the same palatal plosive phonemes which Latvian writes as "ģ" and "ķ" respectively.
   BULLET::::- Alveolar or retroflex approximant (as in most accents of English—with minute differences): The front part of the tongue approaches the upper gum, or the tongue-tip is curled back towards the roof of the mouth ("retroflexion"). No or little friction can be heard, and there is no momentary closure of the vocal tract. The IPA symbol for the alveolar approximant is and the symbol for the retroflex approximant is . There is a distinction between an "unrounded retroflex approximant" and a "rounded" variety that probably could have been found in Anglo-Saxon and even to this day in some dialects of English, where the orthographic key is "r" for the unrounded version and usually "wr" for the rounded version (these dialects will make a differentiation between "right" and "write"). Also used as a rhotic in some dialects of Armenian, Dutch, German, Brazilian Portuguese (depending on phonotactics).
   BULLET::::- "Bunched" or "Molar" R: "bunched-tongue" alveolar approximant (occurs in Southern American English and some Midwestern and Western American English most strongly); in fact, there is often a continuum of possible realizations for the postalveolar approximant within any single dialect from a more apical articulation to this more bunched articulation
  
  BULLET::::- "Velar" R: velarized alveolar approximant (occurs in conservative Irish English)
  
  BULLET::::- "Retroflex" R: retroflex approximant (occurs in some American and most Irish English, including Northern Irish English)
   BULLET::::- PIE *penkʷe 'five' → Latin "quīnque"; Old Irish "cóic"
  
  BULLET::::- PIE *perkʷu- 'oak' → Latin "quercus"; Goidelic ethnonym "Querni", in northwest Hispania "Querquerni".
  
  BULLET::::- PIE *pekʷ- 'cook' → Latin "coquere"; Welsh "pobi" (Welsh p is from Proto-Celtic *kʷ)
  
  A number of other similarities continue to be pointed out and debated.
  
  The "r"-passive (mediopassive voice) was initially thought to be an innovation restricted to Italo-Celtic until it was found to be a retained archaism shared with Hittite, Tocharian, and possibly the Phrygian language.
  
  Section::::Further reading.
   BULLET::::- Uvular (popularly called guttural r): The back of the tongue approaches the soft palate or the uvula. The standard Rs in Portuguese, French, German, Danish, and Modern Hebrew are variants of this rhotic. If fricative, the sound is often impressionistically described as harsh or grating. This includes the uvular approximant, voiced uvular fricative, voiceless uvular fricative, and uvular trill. In northern England, there were accents that once employed a uvular R, which was called a "burr".
   That is, the vowel letters "ä, ö, ü" have the pronunciations they do in German. "C" is pronounced like English "j", and "j" like English "sh". is pronounced after voiced consonants, for example "bs, ds, gs, ls", as it is in English. "R" and "W" were not found in the original proposal.
  
  Note: The letters "ä", "ö", and "ü" do not have alternative forms such as the "ae", "oe", and "ue" of German, but Schleyer proposed alternate forms "ꞛ", "ꞝ", and "ꞟ" for them, all of which are part of Unicode since version 7.0 released in June 2014:
   The "schwa indogermanicum" symbol is sometimes used for a laryngeal between consonants, in a "syllabic" position.
  
  Section::::Phonemic inventory.:Consonants.:Sonorants.
  
  In a phonological sense, sonorants in Proto-Indo-European were those segments that could appear both in the syllable nucleus (i.e. they could be syllabic) and out of it (i.e. they could be non-syllabic). PIE sonorants are the liquids, nasals and glides: , all grouped with the cover symbol "R".
   BULLET::::- The voiceless stops , and are regularly noted by "p", "t" and "k" respectively: "paska" "Easter" (from the Greek ), "tuggo" "tongue", "kalbo" "calf".
  
  BULLET::::- The letter "q" is probably a voiceless labiovelar stop, , comparable to the Latin "qu": "qiman" "to come". In later Germanic languages, this phoneme has become either a consonant cluster of a voiceless velar stop + a labio-velar approximant (English "qu") or a simple voiceless velar stop (English "c, k")
   The rhotic consonant is dropped or vocalized under similar conditions in other Germanic languages, notably German, Danish and Dutch from the eastern Netherlands (because of Low German influence) and southern Sweden (possibly because of its Danish history). In most varieties of German (with the notable exception of Swiss Standard German), in the syllable coda is frequently realized as a vowel or a semivowel, or . In the traditional standard pronunciation, this happens only in the unstressed ending "-er" and after long vowels: for example "besser" , "sehr" . In common speech, the vocalization is usual after short vowels as well, and additional contractions may occur: for example "Dorn" ~ , "hart" ~ . Similarly, Danish after a vowel is, unless followed by a stressed vowel, either pronounced ("mor" "mother" , "næring" "nourishment" ) or merged with the preceding vowel while usually influencing its vowel quality ( and or are realised as long vowels and , and , and are all pronounced ) ("løber" "runner" , "Søren Kierkegaard" (personal name) ).
   Section::::Characteristics.
  
  In broad transcription rhotics are usually symbolised as unless there are two or more types of rhotic in the same language; for example, most Australian Aboriginal languages, which contrast approximant and trill , use the symbols "r" and "rr" respectively. The IPA has a full set of different symbols which can be used whenever more phonetic precision is required: an "r" rotated 180° for the alveolar approximant, a small capital "R" for the uvular trill, and a flipped small capital "R" for the voiced uvular fricative or approximant.
  