See-you-in-sunday vs. See-you-on-sunday: 違いは何ですか？

• in: General containers (e.g., in the summer, in July, in 2026).
• on: Specific surfaces/points (e.g., on Friday, on July 15th, on my wedding anniversary).
• at: Precise points (e.g., at 9 AM, at midnight, at noon).

This is one of English's more common idiomatic quirks, and it's less about strict logic and more about historical usage. Morning, afternoon, and evening are generally perceived as extended, somewhat fluid durations within a day, hence the in (container) metaphor. Night, however, is often conceptualized as a singular, more distinct period, especially as the absence of daylight. It can be seen as a specific 'point' in the 24-hour cycle or a distinct, unified block. Think of it as a specific time frame when certain activities predominantly occur (at night). While in the night is not strictly incorrect (you might hear it in poetic or literary contexts, or when emphasizing an event that happens *during* the night, e.g., He woke up in the middle of the night), at night is the overwhelmingly common and idiomatic choice for general reference.

This is because next, last, this, and every function as temporal determiners. They inherently specify the time and effectively absorb the function that a preposition like in or on would normally perform. The phrase next Tuesday is already precise enough; adding on (*on next Tuesday*) becomes redundant and grammatically incorrect. These words directly link the event to the specified time. For example, I have a meeting this Friday means I have a meeting on this coming Friday. The determiner makes the preposition unnecessary.

For a direct temporal reference to the day itself, you cannot say in Sunday. It is always on Sunday. The day Sunday is a specific point, not a container in which an event takes place in the same way a month is. The phrase in Sunday's paper is grammatically different. Here, Sunday's functions as a possessive adjective modifying paper, and in refers to the location *within* the newspaper itself, not the day. It means inside the newspaper published on Sunday. This illustrates how prepositions change meaning based on the noun they relate to.

This is a matter of contextual ellipsis and common conversational practice. When the month has already been established in the conversation or is clearly understood by all participants, native speakers often omit it for conciseness. For instance, if you are discussing plans for April, you might ask, Are you free on the 15th? The listener understands that the 15th of April is implied. However, in formal writing or when the month might be ambiguous, it is always better to include the full date to avoid any confusion. This is a characteristic of natural spoken language where shared knowledge allows for shortening.

Yes, English has several such phrases. While the general rules are robust, some expressions are purely idiomatic and must be learned as fixed units. Beyond at night, consider: in time (early enough) vs. on time (punctually); in the past/future vs. on occasion. While on time and in time are related to punctuality and duration respectively, phrases like on purpose or in earnest show how these prepositions can be integrated into fixed expressions that don't directly follow the temporal container/surface logic. These are exceptions you'll encounter as you progress to more advanced levels and are best learned contextually rather than trying to fit them into the in/on time framework.