The only safe rule, therefore, is that which Aristotle mentions in the last chapter of his Topica: not to dispute with the first person you meet, but… - Arthur Schopenhauer

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The only safe rule, therefore, is that which Aristotle mentions in the last chapter of his Topica: not to dispute with the first person you meet, but only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to cherish truth, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong, should truth lie with him. From this it follows that scarcely one man in a hundred is worth your disputing with him. You may let the remainder say what they please, for every one is at liberty to be a fool — desipere est jus gentium.