first principles
noun [ plural ] UK uk/ˌfɜːst ˈprɪn.sə.pəlz/ us/ˌfɝːst ˈprɪn.sə.pəlz/
根本原则，首要原则
the basic and most important reasons for doing or believing something
We seem to have forgotten why we're fighting this campaign - we really need to return to first principles. 我们似乎已经忘记了发起这场运动的目的——我们确实需要回到根本原则上来。