Learn Hardcore Portuguese (Brazil): Quando eu terminar a tarefa, eu vou te avisar. - When I finish the task, I will notify you.

After temporal conjunctions like quando, Portuguese requires the future subjunctive instead of the simple future indicative. The form terminar here is the future subjunctive of terminar for “eu.” Using terminarei would be a simple future indicative, which isn’t used in subordinate clauses introduced by quando for future events.

What is the future subjunctive and when do we use it?

The future subjunctive is a verb mood used to talk about actions that depend on a future condition. It appears after conjunctions such as quando, se, assim que, logo que, etc. For regular –ar verbs like terminar, it looks like the infinitive: terminar. For irregular verbs, you derive it from the third person plural of the preterite (e.g., fizeram → quando fizerem).

Why do we say vou te avisar instead of the simple future avisarei?

Brazilian Portuguese often prefers the periphrastic future—ir conjugated + infinitive—in everyday speech. Vou te avisar (“I’m going to let you know”) sounds more natural and conversational, whereas avisarei (“I will let you know”) is grammatically correct but more formal or literary.

Why is the pronoun te used, and could I use lhe instead?

In vou te avisar, te is the second-person singular direct object pronoun meaning “you.” Avisar takes a direct object (“to notify someone”), so te is appropriate. Lhe is a third-person indirect object pronoun (also used formally for “you” when addressing with você), so it doesn’t fit here.

Why is te placed between vou and avisar? Are there other clitic positions?

In periphrastic future constructions, the pronoun usually precedes the infinitive: vou te avisar (proclisis). In more formal or European Portuguese you might see enclisis (vou avisar-te). Mesoclisis happens in the simple future: avisar-te-ei, though it’s rare in speech.

Do we have to include eu before terminar and vou? Can the pronoun be dropped?

Portuguese is a pro-drop language, so subject pronouns like eu can be omitted when the verb ending makes the subject clear. Quando terminar a tarefa, vou te avisar is perfectly natural, especially in casual conversation.

Is the comma before eu vou te avisar necessary?

Yes. When a subordinate clause (introduced by quando) comes first, you normally separate it from the main clause with a comma. If you invert the order—Eu vou te avisar quando eu terminar a tarefa—the comma becomes optional.

Could I shorten the sentence to Quando eu terminar a tarefa, te aviso?

Absolutely. Quando eu terminar a tarefa, te aviso is a concise, informal version. You drop eu before the verbs and switch vou te avisar to the simple present te aviso, which in Portuguese often carries a future meaning.

What’s the best English translation of avisar in this context—does it mean “warn” or “notify”?

Here, avisar means “to let (someone) know” or “to notify.” It doesn’t carry the stronger sense of “warn” (as in caution); it’s closer to “I’ll let you know.”