DO harsh words lead to violent acts? At a moment when hate speech seems to be proliferating, it’s a question worth asking.

Attorney General Loretta E. Lynch recently expressed worry that heated anti-Muslim political rhetoric would spark an increase in attacks against Muslims. Some claim that last month’s mass shooting in Colorado Springs was provoked by Carly Fiorina’s assertion that Planned Parenthood was “harvesting baby parts”; Mrs. Fiorina countered that language could not be held responsible for the deeds of a “deranged” man. Similar debates have been occasioned by the beating of a homeless Hispanic man in Boston, allegedly inspired by Donald J. Trump’s anti-immigration rhetoric, and by the shooting deaths of police officers in California, Texas and Illinois, which some have attributed to anti-police sentiment expressed at Black Lives Matter protests.

No historian can claim to have insight into the motives of living individuals. But history does show that a heightening of rhetoric against a certain group can incite violence against that group, even when no violence is called for. When a group is labeled hostile and brutal, its members are more likely to be treated with hostility and brutality. Visual images are particularly powerful, spurring actions that may well be unintended by the images’ creators.

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