Purpose
What is someone trying to achieve by doing this?
Significado
Purpose links an action to what someone wants to achieve by doing it. The intended result may or may not happen. Languages can use special words, verb forms, or endings, while some rely on context without a separate purpose marker. Unlike Cause, Purpose looks ahead to a goal rather than explaining what led to the action.
Como identificar
Find the part that answers what someone does the action to achieve, whether or not that goal is reached.
Na tua língua materna
Para followed by an infinitive, the verb form used to name an action, commonly states a goal. Para que introduces a full clause whose verb normally takes the subjunctive (subjuntivo), a form used here for an intended outcome rather than an established fact. An infinitive can also have its own subject, so different subjects do not always require para que.
Passei na feira para comprar fruta.
Vou falar baixo para que o bebê não acorde.
Acorde presents the goal, not something that has already happened.
Deixei a chave na portaria para vocês entrarem.
Entrarem is an infinitive with a plural ending matching vocês.
Na tua língua de aprendizagem
English often uses to followed by the base form of a verb, its form without endings, to show the purpose of an action. So that introduces a purpose with its own subject and often a verb such as can or could. For followed by a noun can show what something is intended for, as in money for lunch.
I went to the library to study.
The same person goes to the library and studies.
I'll leave the key here so that you can get in.
So that allows a different subject: I leave the key, and you get in.
This bag is for wet clothes.
For followed by a noun phrase shows the bag's intended use.
Learners whose language uses the same marker for goals and intended uses may write for study instead of to study. Learners whose language normally expresses purpose with a separate subject and verb may overlook the shorter to + verb form when the same person does both actions.