twenty years collecting further facts and verifying observations to test the theory before he gave it to the world.  A generalization that the republican form of government produces greater peace and prosperity than the monarchical would neglect the obvious exceptions in the Central American republics; and to make it at all tenable the generalization would have to have some such proviso as, “among peoples of Germanic race.”  Even then the exceptions would be more numerous than the cases which would fall within the rule.[39] One must cultivate respect for facts in making theories:  a theory should always be held so tentatively that any new or unnoticed facts can have their due influence in altering it.

Of the errors in reasoning about a cause none is more common than that known by the older logic as post hoc, ergo propter hoc (after this, therefore on account of it), or more briefly, the post hoc fallacy.  All of us who have a pet remedy for a cold probably commit this fallacy two times out of three when we declare that our quinine or rhinitis or camphor pill has cured us; for as a wise old doctor of two generations ago declared, and as the new doctrines of medical research are making clear, in nine cases out of ten nature cures.

Of the same character are the common superstitions of daily life, for example, that if thirteen sit at table together one will die within the year, or that crossing a funeral procession brings misfortune.  Where such superstitions are more than playfully held, they are gross cases of calling that a cause which has no relation to the event.  Here is another example, from a letter to The Nation:[40]

In the last volume of the Shakespeare controversy, the argument presented “To the Reader” seems fairly to be summarized as follows:  The plays are recognized as wonderful; scholars are amazed at the knowledge of the classes in them, lawyers at the law, travelers at the minute accuracy of the descriptions of foreign cities; they show a keen critic of court etiquette and French soldiery; the only possible man of the time with this encyclopedic outlook was Francis Bacon.  Both in the original and in the summary there seems a casual connection implied, namely, that the plays are wonderful because of the knowledge, and because of the knowledge Bacon is the author.  But, stated thus baldly, the fallacy is obvious.  It is not because the author “had by study obtained nearly all the learning that could be gained from books” that the Elizabethans went to see the plays, or that we to-day read them; but it is because there is to be found in them wonderful characterization expressed dramatically, namely, before an audience.  And this audience is what the scholars seem to forget.  For by it is the dramatist limited, since profundity of thought or skill in allusion is good or bad, artistically, exactly in proportion as the thought is comprehended or the allusion understood.