Henry George Eloquently Makes the Case that Correlation Is Not Causation

That a thing exists with or follows another thing is no proof that it is because of that other thing. This assumption is the fallacy post hoc, ergo propter hoc, which leads, if admitted, to the most preposterous conclusions. Wages in the United States are higher than in England, and we differ from England in having a protective tariff. But the assumption that the one fact is because of the other, is no more valid than would be the assumption that these higher wages are due to our decimal coinage or to our republican form of government. That England has grown in wealth since the abolition of protection proves no more for free trade than the growth of the United States under a protective tariff does for protection. It does not follow that an institution is good because a country has prospered under it, nor bad because a country in which it exists in not prosperous. It does not even follow that institutions to be found in all prosperous countries and not to be found in backward countries are therefore beneficial. For this, at various times, might have been confidently asserted of slavery, of polygamy, of aristocracy, of established churches, and it may still be asserted of public debts, of private property in land, of pauperism, or of the existence of distinctively vicious or criminal classes. Nor even when it can be shown that certain changes in the prosperity of a country, of an industry, or of a class, have followed certain other changes in laws or institutions can it be inferred that the two are related to each other as effect and cause, unless it can also be shown that the assigned cause tends to produce the assigned effect, or unless, what is clearly impossible in most cases, it can be shown that there is no other cause to which the effect can be attributed. The almost endless multiplicity of causes constantly operating in human societies, and the almost endless interference of effect with effect, make that popular mode of reasoning which logicians call the method of simple enumeration worse than useless in social investigations.
— Henry George, Protection or Free Trade.