This grammar pattern is used to suggest or ask which is based on the speaker’s presumption or expectation about something, an event, a certain circumstance or situation. When a word stem ends with a consonant except ‘ㄹ’, use ‘-을 텐데’. When a word stem ends with a vowel, use ‘-을 텐데’.
● 무거울 텐데 제가 좀 도와 드릴까요? (It must be heavy. So, can I help you?)
● 자고 있을 텐데 전화하지 맙시다. (He might be sleeping. So, let’s not call.)
● 이미 끝났을 텐데 가지 마. (It must ends already. So, don’t go.)