The "ough" tetragraph, usually representing a pronunciation of roughly , is in fact a word in its own right, though rarely known or used: an exclamation of disgust similar to "ugh". The following are recorded throughout English languages of the world:   The following pronunciations are found in uncommon single words:  The place name Loughborough uses two different pronunciations of "ough": the first "ough" has the sound as in "cuff" and the second rhymes with "thorough". In a generative approach to English spelling, Rollings (2004) identifies twenty main orthographic vowels of stressed syllables that are grouped into four main categories: "Lax", "Tense", "Heavy", "Tense-R". (As this classification is based on orthography, not all orthographic "lax" vowels are necessarily phonologically lax.) For instance, the letter "a" can represent the lax vowel , tense , heavy , or (often allophonically) before |r|. Heavy and tense-r vowels are the respective lax and tense counterparts followed by the letter "r". Tense vowels are distinguished from lax vowels with a "silent" "e" letter that is added at the end of words. Thus, the letter "a" in "hat" is lax , but when the letter "e" is added in the word "hate" the letter "a" is tense . Similarly, heavy and tense-r vowels pattern together: the letters "ar" in "car" are heavy , the letters "ar" followed by silent "e" in the word "care" are . The letter "u" represents two different vowel patterns, one being , the other . There is no distinction between heavy and tense-r vowels with the letter "o", and the letter "u" in the pattern does not have a heavy vowel member. Besides silent "e", another strategy for indicating tense and tense-r vowels, is the addition of another orthographic vowel forming a digraph. In this case, the first vowel is usually the main vowel while the second vowel is the "marking" vowel. For example, the word "man" has a lax "a" pronounced , but with the addition of "i" (as the digraph "ai") in the word "main" the "a" is marked as tense and pronounced . These two strategies produce words that are spelled differently but pronounced identically, as in "mane" (silent "e" strategy), "main" (digraph strategy) and "Maine" (both strategies).