The Sequence of Tenses: Present to Imperfect
When you report what someone said in the past using a reporting verb in a past tense (like a dit, a répondu, or a annoncé), the tense of their original statement must take a step back in time. This grammatical rule is known as the sequence of tenses (la concordance des temps).
If the original quote was in the present tense, it shifts to the imparfait (imperfect) in your reported clause. For instance, if your brother originally said, "I am single," you report it as "He claimed that he was single."
This backshifting rule applies exactly the same way when you are describing past thoughts, beliefs, or knowledge, using verbs like penser (to think), savoir (to know), or croire (to believe).
Matching Perspectives
Just as in English, you must remember to adjust subjects, pronouns, and possessive adjectives so they make sense from the reporter's point of view.
This perspective shift also applies to reflexive pronouns, which must be changed to match the new subject of the reported clause.