To quote from Carroll's "Symbolic Logic": He will reply "Why, it's perfectly correct, of course! And if your precious Logic-book tells you it *isn't*, don'

To quote from Carroll's "Symbolic Logic": He will reply "Why, it's perfectly correct, of course! And if your precious Logic-book tells you it *isn't*, don't believe it! You don't mean to tell me those tourists *need* to run? If I were one of them, and knew the Premisses to be true, I should be *quite* clear that I *needn't* run — and I *should walk*!" And you will reply "But suppose there was a mad bull behind you?" And then your innocent friend will say "Hum! Ha! I must think that over a bit!" You may then explain to him, as a convenient *test* of the soundness of a Syllogism, that, if circumstances can be invented which, without interfering with the truth of the Premisses, would make the Conclusion false, the Syllogism *must* be unsound.