expression, godan verb (-ru, irregular)
Used to acknowledge a fact while implying a contrast or reservation. Often followed by が, けど, or しかし. The は adds a contrastive nuance to である.
See also: である
彼は学生ではあるが、あまり勉強しない。
He is a student, but he doesn't study much.
この計画は良い案ではあるけど、実行
This plan is a good idea, but it's hard to carry out.