What is the use of で here?


In the sentence “レジャーが目的で行く“ what does the で express here? Does に work here? I
was trying to compare it to the 〜しに行く, like 勉強しに行く．I understand that 目的 is a
noun so there is no ます form. What if I want to say “for the purpose of flower
viewing”. Where 花見 can be both a noun and a verb? Do I say “花見をしに行く” or
“花見が目的で行く”？




This で is "the te-form of だ". Since 目的 is a noun, you need a copula (だ). It's
in the te-form to [express "collateral
situation"](https://japanese.stackexchange.com/q/38769/5010). If you know how
歩いて学校へ行く ("go to school on foot") or ハサミを使って紙を切る ("cut paper using scissors")
works, レジャーが目的で行く is constructed in the same way; レジャーが目的で describes how the
following action (行く) is achieved.

You cannot say レジャー **が** 目的 **に** 行く, but you can say レジャー **を** 目的 **に** 行く,
which uses the [`AをBに`
pattern](https://japanese.stackexchange.com/a/73094/5010).

In the case of 花見, you can say one of 花見をしに行く, 花見に行く, 花見を目的に行く, and 花見が目的で行く.

