He who knows only his own ...

He who knows only his own side of the case (argument) knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion
He who knows only his own side of the case (argument) knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion
 John Stuart Mill

Quotes from the same author

Accordingly, France Had Voltaire, and his school of negative thinkers, and England (or rather Scotland) had the profoundest negative thinker on record, David Hume: a man, the peculiarities of whose mind qualified him to detect failure of proof, and want of logical consistency, at a depth which French skeptics, with their comparatively feeble powers of analysis and abstractions stop far short of, and which German subtlety alone could thoroughly appreciate, or hope to rival.
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 John Stuart Mill
What citizens of a free country would listen to any offers of good and skillful administration in return for the abdication of freedom?
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 John Stuart Mill
Men and governments must act to the best of their ability. There is no such thing as absolute certainty but there is assurance sufficient for the purposes of human life.
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 John Stuart Mill
When one's ideas are not challenged, one's ability to defend them weakens.
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 John Stuart Mill
One person with a belief is equal to ninety-nine who have only interests.
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 John Stuart Mill