Özet:

The present study aims to compare PhD dissertations, written by Turkish postgraduate students learning English as a foreign language, categorized based on the academic disciplines, in terms of the use of 4-word lexical bundles. To retrieve recurrent lexical bundles and to make their structural and functional analysis, various disciplines are grouped under two separate groups based on the academic fields such as hard and soft sciences. Also, English-major and non-English-major disciplines are compared to each other to see the variation in use of lexical bundles across disciplines. The findings reveal that ELT dissertations, representative of English-major disciplines, have three and four times as many lexical bundles as the dissertations written in the academic fields of soft and hard sciences, respectively. However, the academic fields produce almost the same number of lexical bundle types, suggesting that soft and hard sciences do not show variation in use of 4-word lexical bundles. With regard to the structural analysis of lexical bundles, it is found that lexical bundles most frequently appear in the syntactic categories of noun phrases and prepositional phrases. As for the functional distribution of lexical bundles, the findings indicate that the vast number of lexical bundles in each group function to be referential expressions