What is the difference between でなくand ではなく？


This is the sentence I have just read:

> 外国へ行くとしたら、ただの旅行ではなく、勉強を 目的として 行きたい。 If I ever have a chance to go abroad
> then I would like to go to study rather than just travel.

The は feels intuitively correct but what purpose does it serve? There are a
number of expressions without the は:

> ～だけでなく…によっても広められている be popularized not only by ~ but also by
>
> ～が必要でなくとも although not in need of
>
> [愛]{あい}でなくてなんだろう if it is not love, what is it? (possibly 愛ではなく、なんだろう？）

I can't explain why は is/is not necessary in these expressions (apart from
"these are 決まり文句" but I wanted to get a better understanding than that if
possible).

I should be very grateful for any insights.




As you may already know は is considered the topic marker. Adding は puts
emphasis on the denial aspect and what becomes before ではなく is generally the
topic of the sentence, omitting は makes _what comes after_ でなく the focus of
the sentence.

A more literal translation of your sentence would be:

> If I ever go abroad, I don't want to travel for just pleasure, I would like
> to go to study.

The emphasis is on the denial aspect.




As you may already know は is considered the topic marker. Adding は puts
emphasis on the denial aspect and what becomes before ではなく is generally the
topic of the sentence, omitting は makes _what comes after_ でなく the focus of
the sentence.

A more literal translation of your sentence would be:

> If I ever go abroad, I don't want to travel for just pleasure, I would like
> to go to study.

The emphasis is on the denial aspect.

