Not (colloquial): chẳng / chả

Chẳng means "not", like không, and sits in the same place, before the verb or adjective: Em chẳng hiểu gì hết. I don't understand a thing. It's stronger and more emotional than không, and often carries a shrug or a complaint.

In Saigon, không is the everyday word. Chẳng comes up for emphasis, above all in set phrases: chẳng ai (nobody at all), chẳng có gì (nothing at all), chẳng bao giờ (never ever). You'll also meet it a lot in songs, books and writing. In Hà Nội, chẳng and its short form chả are ordinary in casual talk: Chả biết. Dunno.

Chẳng doesn't work as a one-word answer. To say "no", use không, or in the South dạ, không. And like không, it doesn't go straight before là: "isn't" with a noun is chẳng phải.

While you're learning, keep không for your own sentences, learn to recognise chẳng and chả, and use chẳng when you want to sound a little exasperated.