This research has the purpose of examining the types and functions of modality expressions that are contained in texts sourced from The Corpus of Contemporary American English (COCA). The researcher employed discourse analysis to analyze the meaning and function of the texts of 112 data. The researcher focused on the system of interpersonal modality in SFL designed by Zhou (2021), which includes modulation types of obligation, conditional permission, societal permission, volition, external ability, and internal ability. The result revealed that the examined texts contain some modulation types such as obligation, conditional permission, societal permission, volition, external ability, and internal ability. Certain functions are included in the types of modulation themselves, like asking for advice, giving advice/tips, giving a command, showing duty, giving an argument, asking for permission, giving permission, getting permission, prohibiting an action, complaining, showing willingness, showing ability, giving a compliment, and giving procedure.
