The Korean Writing SystemSyllablesNounsPredicatesFormal and Informal SpeechPre-Final and Final EndingsSpeech LevelAdding ㅓ or ㅏ to a predicate stemWords with 받침Adding 으 to predicates stemsThe Deferential Speech LevelThe Intimate Speech LevelThe Polite Speech LevelThe Plain Speech LevelThe Honorific Ending 시Irregular PredicatesParticlesThe Subject Particle 가 and 이The object particle 를 and 을The Topic Particle 는 and 은Forming a Sentence이다 and 아니다있다 and 없다NegationPast TensePredicates as ModifiersDeterminersBound NounsExpressing desire with 고 싶다NumbersCountersQuestionsThe Particle 에The Plural Particle 들The Possessive Particle 의The Particle 에서The Particle 도The Particle 부터The Particle 까지The Particle 만

Adding 으 to predicates stems

Some suffixes change based on whether a word has ends in a consonant or vowel. Many suffixes will add the syllable 으 if the word it attches to ends in a consonant. For example, the honorific suffix will become when added to a predicate stem that ends in a consonant.
The predicate stem of 괜찮다 ends in a consonant ㅎ so when combined with the honorific suffix 시, a 으시 will be placed after the predicate stem. Note that becomes in the polite speech level.
Are (you) ok?
In contrast the the predicate stem for 돌아오다 does not have a 받침, so when combined with the honorific suffix 시 the predicate becomes 돌아오시.
When does grandfather return?