How ㅣ and ㅓ Combine
For the regular verbs introduced here, a stem ending in ㅣ takes -어요 because ㅣ is not ㅏ or ㅗ .
When the final ㅣ of the stem meets the initial ㅓ of -어요 , the two vowels commonly contract to ㅕ in pronunciation and spelling. This is a vowel combination, not a rule that simply replaces -어요 with -여요 .
Contracting 마시다
Let's look at the verb 마시다 . The stem is 마시- .
Stem: 마시-
Add ending: 마시- + -어요
Contract: 마시어요 becomes 마셔요 .
Contracting 기다리다
The same rule applies to longer words like 기다리다 . The stem is 기다리- .
Stem: 기다리-
Add ending: 기다리- + -어요
Contract: 기다리어요 becomes 기다려요 .
Common Mistake: Adding 여요 Directly
A common mistake is attaching 여요 directly to the stem and writing 마시여요 or 기다리여요 .
First combine the stem with -어요 : 마시어요 and 기다리어요 . Then ㅣ and ㅓ contract to ㅕ , producing the common forms 마셔요 and 기다려요 . The ending is not changed mechanically from -어요 to -여요 .