Prepositions of Time and Place Error Correction

Start by identifying the size of the time expression. Use "in" for larger periods such as months, years, seasons, and general parts of the day: "in April", "in 2026", "in the evening". Use "on" for days and dates, including day plus part of day: "on Monday", "on 12 May", "on Friday morning". Use "at" for exact points: "at 7:30", "at noon", "at night". In this proofreading exercise, do not just look for a familiar word. Read the whole phrase and ask whether it names a broad period, a specific day, or an exact point.

Some place nouns can take more than one preposition when the meaning changes. "At the library" treats the library as a location or meeting point; "in the library" means physically inside the building. Because both can be natural, a good error-correction item must give a clear cue. This route avoids ambiguous clean items such as simply studying at or in a library unless the sentence fixes the meaning. When proofreading, ask what relationship the sentence describes: inside an area, touching a surface, or being at a specific point. The correct preposition should follow that meaning, not a memorised place word alone.

Leave it unchanged if every preposition matches the meaning. Error-correction practice is not the same as a gap-fill, because the task includes clean sentences and two-error sentences. First check time phrases, then place phrases, then movement or duration phrases. A sentence such as "They met at the library entrance at noon" is correct because the entrance is a specific point and noon is an exact time. Changing either "at" just because another preposition sometimes appears with "library" would make the sentence worse. The skill is to prove that a chunk is wrong before you edit it.