Learn Portuguese (Portugal): Tu fumas agora, mas vais deixar de fumar. - You smoke now, but you are going to quit.

When used on its own, deixar does mean "to leave" or "to let." However, when you combine it with the preposition de and an infinitive verb like fumar, it creates a set phrase that means "to stop" or "to quit" doing an action.

In English we say "stop smoking." Why does Portuguese use fumar (to smoke) instead of an "-ing" word?

After the phrase deixar de, Portuguese always uses the infinitive (the basic, unconjugated dictionary form of the verb). While English switches to an "-ing" form after the word "stop," Portuguese keeps it simple with the infinitive fumar.

How do the three verbs in vais deixar de fumar work together?

This combines two verb patterns you have learned! First is the near future: vais (you are going) connects to the main action. The main action happens to be the phrase deixar de (to stop). Because vais is already conjugated for tu (you), the following verbs (deixar and fumar) stay in their infinitive forms.

Why isn't there another tu before vais?