The form -(으)ㄴ/는 모양이다 expresses your supposition one something or someone based on something you’ve seen yourself or something you’ve heard.
With the form -(으)ㄹ 테니까 you can express the reason as to why you are giving a piece of advice or a suggestion. It is an important form to master.
-(으)ㄹ 텐데 is an important form that expresses what you expect(ed) to happen in the future. You can then tell whether the opposite happened or give more info.
The form -(으)ㄹ걸요 expresses your unconfirmed supposition or assumption or something you are simply uncertain about. You use it in spoken language informally.
-아/어 보이다 is a form that expresses one’s conjecture or feelings based on the outwards appearance of something or someone. It is a very simple form to use.
The expressions 동안, -(으)면서 and -(으)ㄹ 때 appear identical, but there are important differences which you have to keep in might. Let’s explain how they differ.