English, in the course of its progressive evolution and global spread, has had contacts with different languages (Hogg & Denison, 2006) which have led to the emergence of native and non-native varieties spoken in different countries of the world. This, in part, has resulted in variable pronunciations of English lexical items, such as anti- pronounced as /ænti/ or /æntaɪ/ at the segmental level and adult as /'ædʌlt/ or /ə'dʌlt/ at the suprasegmental level of stress (Hogg & Denison, 2006). In addition to this, phonological free variation in English has been motivated by phonetic processes, phonological changes and sociolinguistic factors, among others (Shitara, 1993; Mompean, 2010).

英语在其逐步演变和全球传播的过程中，与不同的语言有过接触（Hogg & Denison，2006），这导致了世界不同国家使用的本地和非本地变体的出现。这在一定程度上导致了英语词汇项目的不同发音，例如在句段级别的反发音为 /ænti/ 或 /æntaɪ/，在超音段级别的成人为 /'ædʌlt/ 或 /ə'dʌlt/压力（霍格和丹尼森，2006 年）。除此之外，英语的语音自由变化还受到语音过程、语音变化和社会语言因素等因素的推动（Shitara，1993；Mompean，2010）。