Canadian raising (also sometimes known as English diphthong raising) is an allophonic rule of phonology in many varieties of North American English that changes the pronunciation of diphthongs with open-vowel starting points. Most commonly, the shift affects /aɪ/ or /aʊ/ , or both, when they are pronounced before voiceless consonants (therefore, in words like price and clout, respectively, but not in prize and cloud). In North American English, /aɪ/ and /aʊ/ usually begin in an open vowel [ä~a], but through raising they shift to [ɐ] , [ʌ] or [ə] . Canadian English often has raising in words with both /aɪ/ (height, life, psych, type, etc.) and /aʊ/ (clout, house, south, scout, etc.), while a number of American English varieties (such as Inland North, Western New England, and increasingly more General American accents) have this feature in /aɪ/ but not /aʊ/. It is thought to have originated in Canada in the late 19th century.
In the U.S., aboot [əˈbut], an exaggerated version of the raised pronunciation of about [əˈbʌʊt], is a stereotype of Canadian English.