In order to explore the specific aspects of ‘grammar inquiry’, which has not been able to derive a single consensus concept, this paper established the 2015 revised Korean textbook corpus and conducted word embedding for the textbook corpus through the Word2Vec model. Then, we tried to examine how ‘grammar inquiry’ is represented, by interpreting the implications of 43 key thinking vocabulary in grammar inquiry through cluster analysis. As a result, this paper formed six clusters for 43 key thinking vocabulary. Through each cluster, it was discovered that ‘recognizing’, ‘excluding’, ‘separating’, ‘permitting’, and ‘connecting’ are key thinking vocabulary that mainly appears in grammar inquiry for a phonological unit. Furthermore, it was confirmed that thinking activities such as ‘including’, ‘limiting’, ‘classifying’, and ‘connecting’ appeared in grammar inquiry for a word unit, and ‘regulating’, ‘applying’, ‘presenting’, ‘referring’, ‘confirming’ and ‘accepting’ are used as major thinking activities in a prescriptive grammar area. In addition, although they did not form a clear cluster, it was found that ‘omitting’, ‘connecting’, ‘speculating’, ‘connecting’, and ‘distinguishing’ are the main thinking activities required in grammar inquiry for a sentence unit, while ‘constructing’, ‘deciding’, and ‘interpreting’ are required in grammar inquiry for a discourse unit.