*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.

“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.”

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.”

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Excellent post … thank you!

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

Brilliant!!

I’m glad you enjoyed it. More logic quotes coming soon, along with some Pythagorean math history, after I recover from my latest bout with the flu bug…

My favorite among the logic quotations you have posted:

“Logic is the art of going wrong with confidence.”

This one made me smile, and I don’t know why?

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