Toegye and Nammyeong have commonalities and differences between them in terms of reading theory. As for reasons for reading books, Toegye did for deeply appreciating Cheonri in the heart, and Nammyeong recommended reading for practical benefits. The differences between them are attributed to their different academic attitudes. Their differences become even bigger in internal reading attitudes than external ones. As for internal attitudes, differences become more prominent in that Toegye and Nammyeong focused on Hahakinsa and Sangdalcheonri, respectively, and that Toegye tried to participate in the universal providence, whereas Nammyeong tried to respond to changes to things. As for reading methods and their values to pursue, Toegye's reading method tried to overcome the experiential limitations through the investigation and expansion of faithfulness and thus sought after Cheondo as Sangdalcheonri, whereas Nammyeong's reading method tried to find logic in Hahakinsa and thus sought after Indo as Sangdalcheonri. The reading theories of the two scholars hold huge significance in the ideological history since the connotations and denotations of Seongron go beyond the scope of scriptures, expressing dialectical and convergent ways of thinking. When it is reminded that Seongron was expressed in the discourse space of reading theories, it is possible to mention that reading theories conceived dialectical and convergent ways of thinking