1.3 Significance of this Book

The significance of this study lies in the following five aspects.First，theoretically，the present book is designed with the assumption that recurrent sentential expressions are no less important than either single words or phrases in serving evaluative purposes and that the idiom principle not only works effectively in English but can be applied equally well in the cross-linguistic context.This is an important line of research in corpus linguistics as well as in ESP（English for Specific Purposes）studies.

Second，methodologically，on the evidence of authentic data extracted from large computerized comparable and translation corpora，this study adopts a bottom-up and frequency-based approach，which enables us to provide a relatively complete description of clausal evaluative devices and to find regularities in co-selection relations.

Third，pedagogically，it can be expected to offer insights for ESP teaching.It will show that the long-standing view that science writing is simply detached，factual and impersonal needs to be moderated.It is also essential that sentential devices in academic texts receive due recognition in ESP writing classes and be treated as important means of the regular inventory of attitudinal expressions.

Fourth，the identification of phraseology-based equivalence between English and Chinese is expected to shed light on important bilingual issues.The findings are expected to provide both challenge and complement to the conventional word-for-word translation and to provide an alternative contextualized translational approach that is believed to be a new insight into the practices of translation.

Finally，this study could have important implications for both dictionary compilation and machine translation.It is the corpus data that help to determine which sentential expressions should warrant inclusion in the dictionary entry and in a bilingual lexicon，so that the equivalence information stored may become more easily retrievable.