1 Introduction

Emphasis was placed on the importance of innovative thinking in educational reform, particularly in the field of foreign language teaching. The research of scholars such as Wen Qiufang points out that critical thinking ability is an important goal of foreign language education and a core task of higher education. The 2020 edition of the "Guidelines for College English Teaching" specifies the teaching objectives of critical thinking ability, including information synthesis, comparison, analysis, and forming personal opinions. As an important tool for language teaching and the implementation of educational policies, the compilation of textbooks is crucial for cultivating critical thinking abilities. Therefore, the examination of national level planned university English textbooks is of great significance for improving students' critical thinking ability.

2 Research Status

The importance of cultivating critical thinking skills on a global scale was discussed, and the current situation and challenges of cultivating critical thinking skills in language education in different countries were pointed out. International research has achieved rich results in theoretical exploration and empirical research on critical thinking ability, but there is relatively little empirical research on textbooks and the cultivation of critical thinking ability. In China, although language education scholars emphasize the importance of critical thinking ability, empirical research is relatively scarce, mainly focusing on the examination of students' critical thinking ability, the cultivation of teachers' critical thinking ability, and the application of the "output oriented method" in teaching practice. This study established a national level planned university English textbook corpus, aiming to scientifically, objectively, and comprehensively present the discourse characteristics of textbooks through corpus analysis, and provide reference for the construction of foreign language textbooks in Chinese universities.

3 Research Design

Based on the Delphi Report, a theoretical framework for the study was constructed, emphasizing the importance of critical thinking skills in foreign language education and highlighting the crucial role of textbooks in cultivating critical thinking. The research design includes two main issues: the speculative representation of the thematic semantic domain in textbook discourse and the distribution characteristics of speculative elements. To comprehensively analyze college English textbooks, a "Speculative English Textbook Corpus" was constructed, which includes twelve sets of "National Plan" textbooks. The research method adopts discourse analysis of corpus linguistics, and uses Wmatrix tool for semantic annotation and analysis to identify significant thematic semantic domains and speculative elements in the textbook. In the study, textbook discourse is the core of analysis, excluding post class exercises and online sections. The reference corpus is the BNC Sampler Written sub library, with the criticality threshold set to LL15.13.

4 Research Results and Discussion

Using Wmatrix4 software to conduct corpus analysis on twelve sets of college English textbooks, 184 key thematic semantic domains were identified. By setting the critical threshold LL15.13, the top 50 key semantic domains are selected and visually displayed in the form of a cloud map. Further merge the secondary and secondary semantic domains into the upper semantic domain, such as categorizing [X2.2+: Knowledgeable], [X2.1: Thought, belief], etc. as "psychological actions and processes". Finally, 19 significant upper semantic domains were obtained, such as pronouns, psychological behavior and processes, human, survival, education, language and communication, science and technology, etc.

5 Conclusion and Inspiration

This study analyzed the speculative elements in twelve sets of "national level planning" university English textbooks through quantitative and qualitative methods. In terms of cognitive ability, textbook selection focuses on topics such as people and society, people and self, which are controversial and cognitively challenging, helping to stimulate learners' dialectical thinking. The key thematic semantic domains include pronouns, psychological behavior, human, survival, education, etc. The discourse focuses on social and academic issues, and empirical research methods are used to cultivate learners' proof thinking patterns. In terms of emotional traits, textbooks focus on learners' emotional experiences and self-regulation judgments. Textbook discourse covers rich elements of critical thinking, which helps cultivate learners' critical thinking abilities. The study provides reflection on the transformation of the form of college English textbooks, suggests the development of digital textbooks, expands the capacity of teaching discourse, and provides more resources and technical support for teachers and students.