Aider vs. assister
The French verbs aider and assister can both be translated as to help or to assist, but they are not always interchangeable. Aider is the general, all-purpose word for to help, while assister is more formal and also has a very common second meaning: to attend.
Aider
A1Aider is the most common and general term for to help. It can be used in almost any context, whether for physical help, emotional support, or assistance with a task. It implies an active and direct contribution to make something easier for someone. The structure is 'aider quelqu'un à faire quelque chose' (to help someone to do something).
Peux-tu m'aider à porter ces valises ?
(Can you help me carry these suitcases?)
J'aide ma petite sœur à faire ses devoirs.
(I help my little sister do her homework.)
Ses paroles m'ont beaucoup aidé à surmonter cette épreuve.
(His words helped me a lot to overcome this ordeal.)
Cette carte aide les touristes à se repérer dans la ville.
(This map helps tourists find their way around the city.)
L'association a pour but d'aider les plus démunis.
(The association's goal is to help the most destitute.)
Assister
B1Assister has two distinct meanings. The first is to assist in a more formal, professional, or technical capacity, where one person acts as a subordinate or provides specialized support. The second, and very common, meaning is to attend or to be present at an event, which is the structure assister à quelque chose. This second meaning is a major difference from aider.
Un jeune avocat assiste le procureur durant le procès.
(A young lawyer assists the prosecutor during the trial.)
Le chirurgien est assisté par plusieurs infirmières pendant l'opération.
(The surgeon is assisted by several nurses during the operation.)
Nous avons assisté à un concert magnifique hier soir.
(We attended a magnificent concert last night.)
Tous les employés doivent assister à la réunion de lundi.
(All employees must attend Monday's meeting.)
J'ai assisté à la cérémonie de remise des diplômes.
(I attended the graduation ceremony.)
Il a assisté, impuissant, à la scène.
(He witnessed the scene, powerless.)
Summary
In essence, use aider for general, everyday helping of any kind. Use assister for formal or professional assisting in a secondary role. Most importantly, remember that assister à means to attend or to be present at an event, which is a very frequent usage of the verb.