"The only security against error is in the discussion of every subject, and the careful examination of all arguments, by which it can be supported or opposed."

"Men are not more zealous for truth than they often are for error, and a sufficiently frequent repetition of error, if not contradicted, passes for truth."

"The only source of improvement is liberty, combined with the power of individuals to think for themselves."

"The liberty of the individual must be thus far limited; he must not make himself a nuisance to other people."

"A person should be free to do as he likes in his own concerns; but he ought not to be free to do as he likes in acting for other people, under the pretext that the affairs of other people are his own …"