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We have no other notion of cause and effect, but that of certain objects, which have been always conjoined together, and which in all past instances have been found inseparable.

我们对于因果没有别的概念，只有某些对象的因果概念，它们总是联系在一起的，而且在过去的一切事例中都被认为是不可分割的。

— David Hume 大卫·休谟