passer au peigne fin

You use this phrase as a verb. It describes an action of searching or reviewing. You can use it for physical searches, like looking for lost keys. You can also use it for mental or professional tasks. For example, a lawyer might check a contract this way. Just remember to conjugate the verb passer to match who is doing the searching. If you did it yesterday, use j'ai passé. If you are doing it now, use je passe.

This is a great phrase for the workplace. Use it when you want to impress your boss with your diligence. It also works perfectly in mystery stories or police dramas. Use it when you’ve lost something important at home. It fits well when you are analyzing a complex situation with friends. It conveys a sense of seriousness and high effort. It says, "I am being very careful."

Don't use this for a quick check. If you just peeked in your bag, don't say this. It implies a long, exhausting process. Also, avoid using it for people's feelings. You wouldn't "comb through" a person's soul in a casual chat. It’s mostly for objects, data, or physical spaces. If you use it for a five-second task, you’ll sound sarcastic or dramatic. Save it for the big deep-dives.

French culture places a high value on precision and "le travail bien fait" (work well done). This idiom reflects that national pride in being thorough. It has been used for centuries to describe police investigations. The image of the peigne fin (fine comb) is universal. It suggests that even the smallest "lice" or "knots" of error will be caught. It’s a classic metaphor that hasn't aged a day.

You might hear fouiller de fond en comble. This means to search from bottom to top. It’s very similar but focuses more on a physical building. Another one is scruter à la loupe, which means to look through a magnifying glass. However, passer au peigne fin remains the most popular choice for general thoroughness. It sounds smart and reliable without being too stuffy.