Why use で in「私でよければ入部させてください」?


What's the difference between these sentences:

  * 私 **で** よければ入部させてください

  * 私 **は** よければ入部させてください

  * 私 **を** よければ入部させてください

I was watching the first episode of _K-On!_ anime and I saw this line

> 私でよければ入部させてください.

The English subs translated to

> If it's okay with you I'd like to join the club.

The part that confused me was the **私で**. I got as far as understanding that
the person that is doing the "allowing" is the person being spoken to, the
club leader meaning the verb is being applied to an unseen subject but I still
don't understand why mark the person being allowed with で. It makes no sense
to me.




**～でいい** (or ～で大丈夫, etc) is an expression that means "～ is acceptable (if not
ideal)". I think this is something you can learn by rote. See:

  * [What is the difference between それでいい and それがいい here?](https://japanese.stackexchange.com/q/17851/5010)
  * [Maggie Sensei: Noun + で(も）いい VS +がいい](https://maggiesensei.com/2014/05/20/%E3%80%9C%E3%81%A7%E3%81%84%E3%81%84-%E3%80%9C%E3%81%A7%E3%82%82%E3%81%84%E3%81%84%E3%80%80vs%E3%80%80%E3%80%9C%E3%81%8C%E3%81%84%E3%81%84-de-ii-demo-ii-vs-ga-ii/)

So the literal translation is:

> 私でよければ入部させてください。  
>  If I'm acceptable (to you), let me join the club.

And the implication of the first half is "although I may not be
perfect/ideal". Something like this is said when the speaker is trying to be
humble or when she is not very confident.

私はよければ is ungrammatical simply because は is not allowed in subordinate
clauses.

私をよければ入部させてください means "Let me, if it's okay, join the club." The word order is
not very natural but it still can be parsed as a variation of よければ私を入部させてください
("If it's okay, let me join the club"). This no longer has the original
implication of "although I may not be perfect"; the speaker understands she is
not the decision maker, but she is thinking she will serve as a suitable
member.




**～でいい** (or ～で大丈夫, etc) is an expression that means "～ is acceptable (if not
ideal)". I think this is something you can learn by rote. See:

  * [What is the difference between それでいい and それがいい here?](https://japanese.stackexchange.com/q/17851/5010)
  * [Maggie Sensei: Noun + で(も）いい VS +がいい](https://maggiesensei.com/2014/05/20/%E3%80%9C%E3%81%A7%E3%81%84%E3%81%84-%E3%80%9C%E3%81%A7%E3%82%82%E3%81%84%E3%81%84%E3%80%80vs%E3%80%80%E3%80%9C%E3%81%8C%E3%81%84%E3%81%84-de-ii-demo-ii-vs-ga-ii/)

So the literal translation is:

> 私でよければ入部させてください。  
>  If I'm acceptable (to you), let me join the club.

And the implication of the first half is "although I may not be
perfect/ideal". Something like this is said when the speaker is trying to be
humble or when she is not very confident.

私はよければ is ungrammatical simply because は is not allowed in subordinate
clauses.

私をよければ入部させてください means "Let me, if it's okay, join the club." The word order is
not very natural but it still can be parsed as a variation of よければ私を入部させてください
("If it's okay, let me join the club"). This no longer has the original
implication of "although I may not be perfect"; the speaker understands she is
not the decision maker, but she is thinking she will serve as a suitable
member.

