Is the で in という理由だけで a form of だ or the instrumental particle?


I'm trying to figure out how to say "Maybe it's just because ____, but..." in
Japanese, but I'm not sure how to place 'just because' in its own clause that
way.

If I'm not mistaken, the expression '____という理由だけで' roughly translates to 'just
because ____'. However, since I've only ever seen it used as part of a
sentence about something else, like '友達がその本を推薦したという理由だけで読んだ', I can't tell
whether the で in it acts as a particle, or the te-form of the copula.

Obviously, this is a problem when I'm trying to use the expression as a clause
to add が to in my sentence. Does anyone know the proper way to do so?




The use of で here fits the second
[Wiktionary](https://en.wiktionary.org/wiki/%E3%81%A7) definition:

> with, by, using: indicating the means by or with which something happens

The で here attaches to 理由, rather than だけ. 'Via' and 'per', and 'for' could
also be suitable translations given the right context.

〇〇[という理由で](https://ejje.weblio.jp/content/%E3%81%A8%E3%81%84%E3%81%86%E7%90%86%E7%94%B1%E3%81%A7)
&
〇〇[というわけで](https://ejje.weblio.jp/content/%E3%81%A8%E3%81%84%E3%81%86%E3%82%8F%E3%81%91%E3%81%A7)
For that reason; on the grounds of _____.

I assume you want to add が to mean 'but'. If you show the specific sentence
that you have in mind and attempt your own translation a fruitful answer may
emerge.




The use of で here fits the second
[Wiktionary](https://en.wiktionary.org/wiki/%E3%81%A7) definition:

> with, by, using: indicating the means by or with which something happens

The で here attaches to 理由, rather than だけ. 'Via' and 'per', and 'for' could
also be suitable translations given the right context.

〇〇[という理由で](https://ejje.weblio.jp/content/%E3%81%A8%E3%81%84%E3%81%86%E7%90%86%E7%94%B1%E3%81%A7)
&
〇〇[というわけで](https://ejje.weblio.jp/content/%E3%81%A8%E3%81%84%E3%81%86%E3%82%8F%E3%81%91%E3%81%A7)
For that reason; on the grounds of _____.

I assume you want to add が to mean 'but'. If you show the specific sentence
that you have in mind and attempt your own translation a fruitful answer may
emerge.

