〜もんじゃない・ものじゃない

Not something that...; It's not appropriate to...

1. Overview

「〜もんじゃない」 is a colloquial expression used to indicate that something is not permissible, appropriate, or acceptable. It often carries a sense of admonishment or disapproval regarding a certain action or behavior.

2. Structure

• Verb (dictionary form) + もんじゃない
• Noun + もんじゃない

3. Usage Explanation

• Indicating disapproval: This structure is commonly used to express that an action should not be taken or is inappropriate.

• Casual tone: The phrase is informal and often used in conversations among friends or in casual contexts.

4. Example Sentences

1. そんなに早く帰るもんじゃないよ。
   (You shouldn't go home that early.)

2. 子供の前でそんなことを言うもんじゃない。
   (It's not appropriate to say such things in front of children.)

3. お金を無駄遣いするもんじゃない。
   (You shouldn't waste money like that.)

4. 人を傷つけるようなことを言うもんじゃない。
   (You shouldn't say things that hurt others.)

5. そんなに簡単にあきらめるもんじゃない。
   (It's not something you should give up on so easily.)

5. Key Points to Note

• Casual usage: This expression is primarily used in spoken language and informal settings.

• Conveys a strong opinion: It indicates a strong sense of what is considered right or wrong, often reflecting the speaker's values or beliefs.

6. Similar Grammar

• 〜べきではない: A more formal way to express that something should not be done.
  • Example: そんなことをするべきではない。
    (You should not do such a thing.)

7. Alternative Grammar

• 〜はずがない: Indicates that something is impossible or unlikely, though it doesn't carry the same admonitory tone.
  • Example: 彼がそれを知っているはずがない。
    (There’s no way he knows that.)

8. Summary

「〜もんじゃない」 is an informal expression used to convey disapproval or that something is not appropriate or acceptable. It is commonly used in casual conversations and reflects the speaker's strong opinion on a particular behavior or action.