Grammar
-(으)시- + -어요
honor the subject
Form
Verb/adjective stem + -(으)시- + polite ending — subject honorific.
Function
Shows respect to the person being talked about, regardless of the exact age difference.
Why this form?
-아/어요 (“neutral polite ending”) — Is polite to the listener but does not grammatically honor the subject.
Register and nuance
Subject honorification and politeness toward the listener are separate choices.
Forms not to confuse
-아/어요
괜찮아요? — Are you okay?
Examples
괜찮으세요? — Are you all right?
선생님은 어디 계세요? — Where is the teacher?