L'IDÉE À RETENIR
Pensez du petit au grand : at pour les heures précises, on pour les jours et dates, in pour les périodes longues comme mois et années.

01at: points on the clock
Use at for precise points: clock times, mealtimes treated as points, and festival moments. At 7 o'clock, at noon, at midnight, at night, at Christmas — each one answers the question exactly when. Think of at as a pin dropped on the timeline.
The meeting starts at 10 a.m.
at + clock time
The meeting starts at 10 a.m.
02on: days and dates
Use on for days of the week and calendar dates: on Monday, on May 1st, on Christmas Day. When a date includes the day, on wins — on Monday morning, on the weekend (American) — because the day is the anchor. If you can circle it on a calendar page, reach for on.
Her birthday is on May 1st.
on + date
Her birthday is on May 1st.
03in: longer stretches
Use in for months, seasons, years, and parts of the day: in July, in summer, in 2026, in the morning. These are containers of time rather than points — you are somewhere inside the period. Centuries and decades follow the same logic: in the 1990s.
Watch the famous pair: arrive on time means punctual, while arrive in time means early enough to do something — in time for dinner, in time to help. And drop the preposition entirely before this, last, next, every, yesterday, and tomorrow: see you next Monday, not on next Monday.
She was born in 2019.
in + year
She was born in 2019.
04Try a week of your life
Write seven lines about your week using all three: at 7:30, on Tuesday, in the evening. Then add one deadline with by — finish this by Friday — and notice how by means no later than, not at that moment. Keeping your own examples next to each other makes the small-to-big picture stick.
À VOUS
Faites le lien.
Lisez la situation avant de choisir. Le pourquoi compte autant que la réponse.
Pour aller plus loin
Nous créons ces exemples avec l'aide de l'IA. L'usage dépend du contexte ; ces schémas ne couvrent pas tout. Poursuivez avec les références.
Un peu de répétition. Un lien plus fort.
Poursuivez avec des exercices ciblés et la révision des erreurs dans l'appli.
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