Let’s Play Math!

Photo by Brian - Progressive Spin.

Logic is the science of making valid deductions and proofs — and it is also a fruitful topic for blackboard quotes. Here are a few of my favorites:

You can only find truth with logic if you have already found truth without it.

— G. K. Chesterton
The Man Who Was Orthodox

“When I use a word,” Humpty Dumpty said, in a rather scornful tone, “it means just what I choose it to mean — neither more nor less.”
“The question is,” said Alice, “whether you can make words mean so many different things.”
“The question is,” said Humpty Dumpty, “which is to be master — that’s all.”

— Lewis Carroll
Through the Looking Glass

Logic, like whiskey, loses its beneficial effect when taken in too large quantities.

— Lord Dunsany
In J. R. Newman (ed.), The World of Mathematics

Logic is the art of going wrong with confidence.

— Morris Kline
In N. Rose, Mathematical Maxims and Minims

Logic is the hygiene the mathematician practices to keep his ideas healthy and strong.

— Hermann Weyl
The American Mathematical Monthly, November, 1992.

Alice laughed: “There’s no use trying,” she said; “one can’t believe impossible things.”
“I daresay you haven’t had much practice,” said the Queen. “When I was younger, I always did it for half an hour a day. Why, sometimes I’ve believed as many as six impossible things before breakfast.”

— Lewis Carroll
Alice in Wonderland

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• Math Quotes II: The Ultimate Goal of Mathematics
• Math Quotes VI: Beauty in Mathematics
• Quotations VIII: The Essence of Mathematics
• Quotations XIV: The Joy of Mathematics
• Quotations XV: More Joy of Mathematics