A conjunction used to connect a statement with a contrasting or contradictory one (equivalent to "but," "however"). Common in both speech and writing, somewhat formal or literary.
彼は有能だ。だが、人付き合いが苦手だ。
He is capable. However, he is poor at getting along with people.
計画はいい。だが、予算が足りない。
The plan is good. But the budget is insufficient.
約束は守った。だが、それを理由に責めるのはおかしい。
I kept my promise. Still, it's strange to blame me for that.
彼女は来ると言った。だが、結局現れなかった。
She said she'd come. Yet in the end she didn't show up.