在读《美国货币史》和《科学说需求》的时候，在正文前都写着马歇尔的一句话，好奇之下去查找了解，发现出自这篇，现与诸君分享此经典，每每读来都颇多感悟，掩卷沉思，受益良多。

2021.3.11  

开卷有益！

现附上该句原文：

Experience in controversies such as these brings out the impossibility of learning anything from facts till they are [167/168] examined and interpreted by reason; and teaches that the most reckless and treacherous of all theorists is he who professes to let facts and figures speak for themselves, who keeps in the back ground the part he has played, perhaps unconsciously, in selecting and grouping them, and in suggesting the argument post hoc ergo propter hoc.

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