Hello,
I recently saw this phrase in a warning sign:
みんなで川・ 公園を美しく!雨の日は、川の水が急に増えて危ないので、入らないで下さい。
I understand the general sense of the phrase, but don't quite get the use of the で particle in the beginning: みんなで
What's it doing there? I suspect it's being used in a "by means of" sense. As in "英語で話す" or "箸で食べる". Is it something like people make the river/park beautiful? Ie, is it "by means of the people('s actions)" that the river/park is beautiful?
みんなと suggests the existence of the subject. Someone is saying that he/she does so together with everyone. で indicates the state, as I wrote, so みんなで means to do so with all the people together, not with the speaker/writer.