When to Use "On" as a Preposition of Time?

You should use the preposition "on" primarily for specific days, dates, and particular parts of a day that are clearly identified.

Understanding "On" in Time Prepositions

The preposition "on" helps pinpoint exact moments or periods on a calendar. It serves to specify rather than generalize.

Specific Days and Dates

The most common use of "on" for time is with specific days of the week, precise dates, or holidays treated as single days.

• Days of the Week: When referring to any day from Monday to Sunday.
  • We have a meeting on Monday.
  • The store is closed on Sundays.
• Specific Dates: For full dates that include the day, month, and/or year.
  • Her birthday is on March 15th.
  • The event will take place on December 25, 2024.
• Specific Holidays/Special Days: When referring to a particular named day.
  • Families gather on Christmas Day.
  • They typically exchange gifts on their anniversary.

Specific Parts of a Day

While the preposition "in" is commonly used for general parts of the day (e.g., in the morning, in the afternoon, in the evening, in the night), "on" is used when these parts of the day become specific or are described in a particular way. This distinction is crucial for clear communication.

Consider these examples:

• The ship left the harbour on the morning of the ninth of November. (Here, "morning" is specified by the date.)
• We had a productive discussion on the afternoon of the summit. (The "afternoon" is clearly identified by the event.)
• I remember seeing him on that cold, dark evening. (The "evening" is described in a specific manner.)
• The performance begins on the night of the premiere. (The "night" is particularized by the event.)

In contrast, if you are referring to the part of the day generally, without specific modifiers, you would use "in":

• I always work best in the morning. (general)
• I often get tired in the afternoon. (general)

"In" vs. "On" for Parts of the Day: A Comparison

The choice between "in" and "on" for "morning," "afternoon," "evening," and "night" depends on whether the reference is general or specific.