Mental slavery is mental death, and every man who has given up his intellectual freedom is the living coffin of his dead soul. – Robert Ingersoll, Individuality

I had an immense advantage over many others dealing with the problem inasmuch as I had no fixed ideas derived from long-established practice to control and bias my mind, and did not suffer from the general belief that whatever is, is right. – Henry Bessemer (discovered new method of producing steel)

The public buys its opinions as it buys its meat, or takes in its milk, on the principle that it is cheaper to do this than to keep a cow. So it is, but the milk is more likely to be watered. – Samuel Butler, Notebooks, 1912

Keep your minds open, but not so open that your brains fall out. – Walter Kotschnig, c.1940