"Proved right should be capable of being vindicated by right means as against the rude i.e. sanguinary means. Man may and should shed his own blood for establishing what he considers to be his right. He may not shed the blood of his opponent who disputes his 'right'."

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Commemoration of Gilbert of Sempringham, Founder of the Gilbertine Order, 1189 Some there are who presume so far on their wits that they think themselves capable of measuring the whole nature of things by their intellect, in that they esteem all things true which they see, and false which they see not. Accordingly, in order that man's mind might be freed from this presumption, and seek the truth humbly, it was necessary that certain things far surpassing his intellect should be proposed to man by God.

— Thomas Aquinas