A petard was a medieval bomb. To be “hoisted by one’s own petard” is to be blown up by one’s own bomb. People utter petards when they use words that destroy their own arguments (self-defeating statements). Here are a few humorous examples:
• “I plan to be more spontaneous.”
• “All extremists should be shot.”
• “Nostalgia isn’t what it used to be.”
Moral relativists create petards by stating absolutes or by making value judgments because absolutes and value judgments defy their worldview. Since they claim that moral absolutes don’t exist (truth is a “gray zone”) but use absolute terms such as the following list, their arguments are self-defeating:
• “all/none (no one)”
The way to respond to petards is simply to apply the speaker’s statement to itself, thereby letting the argument blow itself up. Look at these examples:
• “All truth is relative.” < Is that statement a relative truth?
• “There is a gray zone between black and white and that’s where most of the truth lives.” > Is that statement gray (sort of true), or black and white (absolutely true)?
• “Everyone should believe in relative truth.” < Is that statement a relative truth?
• “No one has the whole truth.” < Is that statement the whole truth?
• “Truth should be decided by each individual.” < Are you deciding that truth for me?
• “That’s true for you but not for me.” < Is that statement only true for you or for everybody?
But ending the conversation here only creates contempt. Explain that you are not trying to be a wise guy, but instead that you are trying to show how everyone uses absolutes; that’s just the way truth works.