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Ch. I. § 3.]

The chief use you will find, in such Logical skill as this Game may teach you, will be in detecting 'Fallacies' of these two kinds.

The first kind of Fallacy——'Fallacious Premisses' you will detect when, after marking them on the larger Diagram, you try to transfer the marks to the smaller. You will take its four compartments, one by one, and ask, for each in turn, "What mark can I place here?"; and in every one the answer will be "No information!", showing that there is no Conclusion at all. For instance,

"All soldiers are brave;
Some Englishmen are brave.
∴ Some Englishmen are soldiers."

looks uncommonly like a Syllogism, and might easily take in a less experienced Logician. But you are not to be caught by such a trick! You would simply set out the Premisses, and would then calmly remark "Fallacious Premisses!": you wouldn't condescend to ask what Conclusion the writer professed to draw——knowing that, whatever it is, it must be wrong. You would be just as safe as that wise mother was, who said "Mary, just go up to the nursery, and see what Baby's doing, and tell him not to do it!"

The other kind of Fallacy——'Fallacious Conclusion'——you will not detect till you have marked both Diagrams, and have read off the correct Conclusion, and have compared it with the Conclusion which the writer has drawn.