Almost everybody would approve of physical violence, even killing, in easily imagined conditions. Suppose you had come upon Guy Fawkes in the very act of firing the train, and suppose you could only have prevented the disaster by shooting him; most pacifists, even, would admit that you would have done right to shoot. The attempt to deal with the question by abstract general principles, praising acts of one type and blaming acts of another, is futile; we must judge the exercise of power by its effects, and we must therefore first make up our minds to what effects we desire.
Source: Power, 1938.
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