Non-defining relative clauses in French
French lets you add background about an already identified person or thing inside a sentence. In these examples, qui and que distinguish the clause's subject from its direct object, rather than people from things. The Anna example uses informal tu, suitable with someone you address familiarly; the relative pronouns themselves do not mark formality.
Qui as a subject; ce qui for a whole statement
Adding background about people: qui or que
Nom déjà identifié, qui information complémentaire, proposition principale.
Ma sœur, qui habite à Paris, sera de passage ce week-end.
Anna, que tu as rencontrée hier, déjeune avec nous.
Adding background about things: qui or que
Nom déjà identifié, qui/que information complémentaire, proposition principale.
La gare, qui a ouvert l’an dernier, est déjà trop petite.
Ma voiture, que j’ai achetée le mois dernier, est encore en panne.
Adding a consequence or reaction with ce qui
Proposition principale, ce qui conséquence ou commentaire.
La réunion s’est terminée plus tôt, ce qui nous a laissé le temps de discuter du problème.
The meeting finished early, which gave us time to discuss the problem.
Ils ont encore changé la date, ce qui est vraiment agaçant.
Attach the background to its noun and choose qui or que
Place the extra clause immediately after the noun it describes, with commas around it when the main sentence continues afterward. In “Ma sœur, qui habite à Paris, sera de passage ce week-end.”, qui is the subject of habite, and the visit remains the main point. Qui also serves as a subject for things, as in “La gare, qui a ouvert l’an dernier, est déjà trop petite.”
Use que when the person or thing is the direct object inside the extra clause, as in “Anna, que tu as rencontrée hier, déjeune avec nous.” Unlike an object relative pronoun in some English clauses, French que cannot be omitted. In rencontrée and achetée, the final e marks agreement with the feminine direct object placed before the past participle with avoir.
Ma sœur, qui habite à Paris, sera de passage ce week-end.
La gare, qui a ouvert l’an dernier, est déjà trop petite.
Distinguish a comment on an event from a description of a noun
In “La réunion s’est terminée plus tôt, ce qui nous a laissé le temps de discuter du problème.”, ce qui refers to the whole event of the meeting finishing early. English uses “which” here, but French needs ce qui because no single preceding noun is its reference and the expression is the subject of the following verb. The same structure introduces an evaluation in “Ils ont encore changé la date, ce qui est vraiment agaçant.”
Use a comma before ce qui and a slight pause in speech. For background attached to a noun, commas similarly separate the extra information; without them, the clause can instead identify which person or thing you mean. Ce qui is suitable in both conversation and formal writing.
La réunion s’est terminée plus tôt, ce qui nous a laissé le temps de discuter du problème.
The meeting finished early, which gave us time to discuss the problem.
Ils ont encore changé la date, ce qui est vraiment agaçant.