Purpose
What is someone trying to achieve by doing this?
المعنى
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.
طريقة التعرّف عليه
Find the part that answers what someone does the action to achieve, whether or not that goal is reached.
في اللغة الأم
Arabic expresses purpose with لِـ followed by a noun naming the intended activity, or with لِـ, كي, or لكي followed by a verb. After these purpose markers, a present-form verb takes the subjunctive (manṣūb), a form often ending in -a instead of -u. The expression states an intended goal, whether or not it is achieved.
أذهبُ إلى المكتبةِ لأدرسَ بهدوءٍ. (Adhhabu ilā al-maktabati li-adrusa bi-hudūʾ.)
لِـ introduces the goal, and أدرسَ has the subjunctive ending.
اتصلتُ بمريمَ لكي أسألَها عن الموعدِ. (Ittaṣaltu bi-Maryama li-kay asʾalahā ʿan al-mawʿid.)
وفّرتُ المالَ لشراءِ حاسوبٍ. (Waffartu al-māla li-shirāʾi ḥāsūb.)
Here لِـ is followed by a noun naming the intended activity.
في اللغة قيد التعلم
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.