Perhaps: có lẽ

Có lẽ means "perhaps" or "probably". It's a gentle guess, and it usually opens the sentence: Có lẽ anh nói đúng. Perhaps you're right. It can also come after the person or thing, especially before là: Đây có lẽ là quán phở ngon nhất Sài Gòn. This is probably the best phở place in Saigon.

The có in có lẽ isn't the có of có … không. The sentence stays a statement, with nothing added at the end.

Có lẽ is a polite way to soften bad news or a refusal: Có lẽ mai em không đi được. I might not make it tomorrow. As a reply, Có lẽ vậy means "perhaps so" (in Hà Nội, Có lẽ thế).

It sits between its neighbours. Chắc is more confident and belongs to speech: Chắc ảnh quên rồi, he's probably forgotten. Có lẽ is softer, and just as much at home in writing. Có thể at the start means "maybe, it's possible", a weaker guess. And hình như (it seems) is for what you've heard or half remember.