1) Ask someone to demonstrate their argument.
People these days love to make bold claims. "You're wrong! It's this way!" or, "I believe this and that's the way it is!" Many times, this is because we are taught simply to repeat what we are told rather than being able to defend what we are told.
Recently I went into a conversation with someone who, wanting to disprove my argument, accused me of mishandling scripture. I asked him to show how I had done so. He refused to answer, so I pressed him again. He again refused to answer, saying that wasn't the topic (even though that was what he was using to say I was wrong). I pressed him again, and he simply ended the conversation then and there.
I heard a story recently of a Jehovah's Witness woman who gave a biblical scholar a long, memorized speech regarding John 1:1 and why they translate it as "the Word was a god" because of the lack of a definite article. The scholar then handed her a Greek New Testament and asked her to show him what a Greek definite article looked like. The woman didn't even know how to hold the book up straight. She had a memorized argument, but when asked to demonstrate the argument, she fell on her face.
2) Ask someone to back up their argument with sources.
If you ask a person this, they might do one of a few things.
- Throw the weight of the evidence upon you. That is, say something like, "Well, you can figure it out," or, "Well, you can do research for yourself." The weight of the evidence falls on the person making the claim. There is a good reason why, in the United States, a charged person is "innocent until proven guilty" - the burden of proof is on the accuser, not the accused.
- Demand you prove a negative. Example: someone claims that their horn scares away burglars, and when asked how they know it does, they reply, "Well, can you prove it doesn't scare away burglars?" This is a cop out because they are: 1) not giving a response; 2) forgetting that by nature you cannot prove a negative.
- Get very, very irate with you. I had one person tell me literally: "I DON'T HAVE TO GIVE YOU ANYTHING!" If a person gets emotional, it's a good sign that their argument has no substance.