The Illegitimate Extension

More generous offerings of excerpts from good books I own; I’ve been moving things on to the new set of shelves I’ve just finished building and unearthing a few delights. Tonight it’s the turn of How to Write, Think and Speak Correctly edited by C.E.M Joad and published quite-a-long-time-ago (there’s no date in it) by Odhams Press.

Sweeping generalizations deserve no mercy and people who rely on them merit all the rebuffs they receive. Provided that an opportunity of questioning them is presented, they are, however, more dangerous than helpful to the controversialist, as they are so open to attack. If only for that reason we should avoid them. The fact that they are dangerous, however, has given rise to a trick of argument known as illegitimate extension.

Suppose you were to maintain against me that: “Some Englishmen are unreasonable.” That is a moderate position which I should find it difficult to assail. I might, therefore, resort to a trick. I might say: “That’s all very well, but if you say some Englishmen cannot be reasonable you ought logically to say all Englishmen are unreasonable.”

In this way I am seeking, illegitimately, to extend your argument until it covers a position which is demonstrably unsound. I am seeking, that is, to manoeuvre you into defending the proposition: “All Englishmen are unreasonable,” a proposition which I can disprove with the greatest of ease.

Taken from the section entitled The Art of Thinking: Some Unfair Tricks of Argument.

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