I am not sure when to use qui and when to use lequel ou laquelle. I would like to have a precise answer.
2 Answers
From https://frenchcrazy.com/2013/12/french-relative-pronouns-dont-qui-que-lequel-ou.html/ :
Qui
Qui can refer to people or things and is used as the subject of a dependent clause. Because qui becomes the subject of the sentence it is always followed by a conjugated verb and must agree in number with the antecedent it is referring to.
« On critique les films qui montrent trop de nudité. » → "People criticize films that display too much nudity."
Lequel/Laquelle
The relative pronoun lequel (and all of its forms) replace a preposition (other than de) and a thing/object in a relative clause. Make sure that the pronoun agrees in both number and gender to whatever it is describing.
« Une langue est un prisme à travers lequel ses usagers sont condamnés à voir le monde. » → "A language is a prism across which its users are condemned to see the world."
I have a partial answer that is not academic but helped me a lot in learning to use lequel as an English speaker.
Effectively, just use lequel whenever you want to replace things like:
- dans (j'ai une boîte dans laquelle je mets tous mes trucs)
- avec (elle est la fille avec laquelle j'ai parlé hier)
- sur (c'est la table sur laquelle il y a un gateâu)
- à traves (c'est la vitrine à traves de laquelle on peut voir le truc) I can't think of any more prepositions but yeah, you get the idea...
Whereas for qui, think of VERBS
- le mec qui a largué sa copine (qui + larguer)
- le prof qui est nul (qui + être)
- le so on so forth
Hope this helps. I am not native speaker so might not be 100 percent correct.