Here is a good definition of pacifism: the quest to overcome evil without doing evil, and without becoming evil oneself.
This definition is inspired from this quotation:
"How, then, can we overcome evil without doing evil -- and becoming evil ourselves? I found myself reluctantly being pushed, simply by the logic of the inquiry, to a position of consistent nonviolence." Walter Wink, The Powers that Be: Theology for a New Millennium, Galilee Doubleday, 1998, pp. 7-8.
5 years ago