Breakdown of Paul et Marie se promènent au bord de la mer.
Questions & Answers about Paul et Marie se promènent au bord de la mer.
Because se promener is a pronominal (reflexive-style) verb in French. It is normally used with a reflexive pronoun:
- je me promène
- tu te promènes
- il/elle se promène
- nous nous promenons
- vous vous promenez
- ils/elles se promènent
In this sentence, the subject is Paul et Marie, which is they, so French uses se promènent.
Even though English often just says Paul and Marie are walking or are taking a walk, French usually keeps the pronoun with this verb.