Really, truly: thật / thật là

Thật means "real, true", and after an adjective it means "really": Ngon thật! It really is good! It confirms something, often what you'd heard or hoped. A friend said the place was good; you taste it and agree. In Saigon it's pronounced thiệt, and chats and dialogue often write it that way: Ngon thiệt!

Before an adjective, use thật là: Hôm nay thật là vui. Today was really fun. It sounds heartfelt, like "truly". Plain thật before the adjective, as in cảnh thật đẹp (truly beautiful scenery), sounds more written. Songs and stories sometimes put the adjective on both sides: vui thật là vui.

On its own, it asks or tells whether something is true: Thiệt hả? Really? (in Hà Nội, Thật à?). Nói thật, … means "to be honest, …".

Compared with rất, which just says "very", thật adds "and I mean it". Quá reacts in the moment; thật agrees or confirms. In writing and formal speech, thật sự means "truly": Tôi thật sự xin lỗi. I'm truly sorry.