This book marks a new development in the field of grammaticalisation studies, in that it extends the field of grammaticalisation studies from relatively homogeneous languages to those possessing well-established and institutionalised second language varieties. In Hypothetical Modality, special reference is made to Singaporean English, a native-speaker L2 dialect of considerable importance in the South-East Asian region, and to the expression in the dialect of hypothetical modality, which appears to be indistinguishable from non-hypothetical modality in terms of the use of preterite or past forms of modal verbs. Within a grammaticalisation framework, a number of factors can be seen to be relevant to an explanation, including substratum and contact features such as tense/aspect marking, levels of lexical retention as an individual (psychological) phenomenon, and the fact that such dialects have a discontinuity in their development. In addition, the book defines pragmatic approaches to the understanding of hypothetical modality, in both diachronic and synchronic terms.