Refers to major issues of principle, where right and wrong are clearly defined.
指带有原则性、根本性的是非问题。
徐迟《歌德巴赫猜想》一页一页的历史写出来了，大是大非，终于有了无私的公论。”
In matters of 大是大非, we must not compromise our principles.
Learn the next connected idiom: 大是大非 (dà shì dà fēi) → 非同寻常 (fēi tóng xún cháng)
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