Learn Hardcore Japanese: betu no hi ni yoyakusimasu. - I will make a reservation for another day.

に marks a specific point in time, so 別の日に means “on a different day.” で would indicate means/method or location of an action, e.g., 電話で予約します “I’ll reserve by phone.” For time expressions like a particular day/date, use に.

Who is the subject? Why is it missing?

Japanese often omits subjects when clear from context. Here it’s most likely “I” or “we.” If you need to state it, you can say 私は別の日に予約します or 私が別の日に予約します for emphasis.

There’s no direct object—what exactly is being reserved?

In Japanese, 予約する by itself can mean “to make a reservation (for the understood thing).” To specify:

レストランを予約します (reserve a restaurant table)
ホテルを予約します (book a hotel)
歯医者の予約をします (make a dentist appointment)

What’s the difference between 予約します and 予約をします?

Both are correct. 予約します is more common and feels lighter/natural. 予約をします is a bit heavier or more formal-textbook-y; it can add clarity or emphasis, especially in careful speech or writing.

Is 予約する transitive? What can be the object?

Yes—予約する is a transitive suru-verb. You can say 席を予約する, ホテルを予約する, チケットを予約する. You can also use the noun pattern 〜の予約をする (e.g., レストランの予約をする).

What’s the nuance difference between 別の, 他の(ほかの), and 違う?

別の: a distinct, alternative one (often “another” in the sense of switching to a different option).
他の(ほかの): “other” among the remaining options in a set.
違う: “different” emphasizing non-sameness; 違う日 is common in speech.
All three can work here; 別の is a very natural choice for proposing an alternative day.

Can I say 別日 instead of 別の日? And what about 別日で?

別日（べつび） is common in schedules/emails (business-like). In everyday speech, 別の日 sounds more natural. For time marking, stick with 別の日に; set phrases like 別日でお願いします exist in business, but に is the safer, standard time marker.

Why is there の after 別? What part of speech is 別?

別 is a noun that can modify another noun with の: 別の日. You’ll also see 別な (especially regionally); 別な日 is acceptable, but 別の日 is more standard and widely taught.

Does します here mean present or future?

Japanese non-past covers both present and future. Context decides whether it’s a decision about the future or a habitual action. In this sentence, it’s naturally understood as a future decision/plan.

How can I adjust the politeness or nuance?

Neutral polite: 別の日に予約します。
More polite/humble: 別の日に予約いたします。
Suggestion: 別の日に予約しましょう。
Casual: 別の日に予約するね／しとくね。
If rebooking: 別の日に予約し直します。

Can I omit に after 日?

Generally no. For a specific day/date, keep に: 別の日に. You can often omit に with relative time words like 明日, 来週, but with 日 + modifier or a calendar date, に is normally required.

Is the word order flexible?

Yes, within limits. These are fine:

別の日に予約します。 (default)
予約は別の日にします。 (topic/focus on the reservation)
別の日に予約をします。 (also okay)
But 予約します、別の日に sounds unnatural in most contexts.

How do I pronounce it?

Read it as: べつのひによやくします (romaji: betsu no hi ni yoyaku shimasu). No pauses/spaces in normal writing or speech; the spacing here is just for learners.

How do I say I want to reschedule to a different day?

予約を別の日に変更したいです。
別の日に予約し直したいです。
Very polite: 予約日時の変更をお願いできますか。

What’s the difference between 予約, 約束, and アポイント?

予約: a booking with a service/place (restaurants, hotels, clinics).
約束: a promise/arrangement with people (meeting a friend).
アポイント（アポ）: a business “appointment” (with a person/company), often used in office contexts.

Are there other common verb collocations with 予約?

Yes:

予約を入れる (to make a reservation; very common in speech)
予約を取る (to get a reservation; commonly used, though some prefer 予約する/入れる to avoid any ambiguity with “取り消す”)
席を押さえる／確保する (to secure a seat)
For canceling, use 予約をキャンセルする／取り消す.