The paper identified and analysed patterns of discourse thematic progression (TP) in Science-Based postgraduate theses abstracts in selected universities in Southwestern Nigeria. It described the linguistic realization of TPs across the identified four motifs of text such as introduction, methodology, findings and conclusion and also discussed the content of texts via the functional categories of texts. One hundred and fifty PhD theses abstracts out of six hundred and three abstracts produced

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... the Sciences of the Obafemi Awolowo University, Ile-Ife, University of Ibadan and University of Lagos were selected through simple random sampling. An analysis of progression of theme and rheme was done on the selected abstracts by adopting the framework of the functional sentence perspective as propounded by Dane's (1970 and and the systemic linguistic approach. The themerheme analysis of texts and their linguistic realization across the identified motifs was done to unravel the content of the abstracts. The findings showed that all TP patterns (Constant TP, Simple Linear TP, Derived TP and Split Rheme TP) featured in the text. The Constant TP predominates the text motifs of texts. These linguistics features largely associated with the Constant TP were the nominal phrases, noun, pronoun, cleft among others. The study concluded that text content, thematic patterns and linguistic features integrate to create meaning in text and one way to understand texts better is to unravel their patterns in texts.