Grammatical usage of "で" in the sample sentence: 「～～で正解だと思います。」


> "Do you mean the red haired boy?" は、「赤毛の男の子のことですか？」 **で** 正解だと思います。

So this is an explanation I got from a Japanese person.

And I wanna understand what does exactly "で" mean here. Why is it not "が"
because it is a positive sentence and all.




The で is broadly _with, by_ as usual. Slightly more precisely, it is 基準(#6
[here](https://dictionary.goo.ne.jp/word/en/%E3%81%A7/#je-50708)), perhaps
材料(#3) is relevant too.

A typical usage is

  * 私はこれでいいです _I'm okay with this_

meaning you are happy with what you have at hand.

Using が sounds excluding other possibilities of translations (as _This **is**
the correct one_). Using で makes it sound like _This is **a** correct
translation_.

* * *

Some other similar usage

  * リンゴはひとつ **で** 十分です One apple is enough
  * コップはみっつ **で** 足ります Three cups will be enough

