The burden of proof is the responsibility someone has to defend or give evidence for his view. Generally, the rule can be summed up this way: Whoever makes the claim bears the burden. The key here is not to allow yourself to be thrust into a defensive position when the other person is making the claim. It's not your duty to prove him wrong. It's his duty to prove his view.(1)
It doesn't matter whether you are discussing theology, philosophy, politics or ethics, the burden of proof rule is a crucial one to remember. It prevents you from being unjustly placed in a defensive position and forces the individual making the claim to carry his own load.
EXAMPLE #1: THERE IS NO GOD!
Perhaps you have been in a conversation or overheard one that goes something like this:
Skeptic: There is no God.
Christian: Really? How do you know that?
Skeptic: Well, how do you know there is a God?
Notice what has happened here. The skeptic started out the conversation by making a truth claim. In this case, he is making the claim "there is no God." The Christian rightly asks the question "How do you know that?" in order for the skeptic to provide justification for his position, as he should. After all, the skeptic is the one making the claim. Therefore, the skeptic bears the burden of proof in this case. But the skeptic doesn't accept it! Instead, he tactfully (and wrongly) attempts to shift the burden of proof to the Christian!
So how should the Christian respond? Should he answer the question? Should he accept the burden of proof? Should he give a three hour lecture on the kalam cosmological argument? No! Why not? Because he is not the one who made the claim. Instead, the Christian should point out to the skeptic that since it is the skeptic who made the claim it is his job to support it. The conversation might continue like this:
Skeptic: Well, how do you know there is a God?
Christian: Wait, hold on a minute. You started out this conversation by making the claim that there is no God. Since you made the original claim, the burden of proof is on you to provide some reasons or evidences as to why you think you are right. I am not going to accept any burden of proof at this point because I have not made any claims. So again, how do you know there is no God?
EXAMPLE #2: THE BURNING BUSH
Here is another scenario. Recently I was speaking with a friend of mine who is Roman Catholic. We began discussing the Roman Catholic doctrine of transubstantiation (a five dollar word for sure, this is the idea that the bread and wine during communion actually become the body, blood, soul, and divinity of Christ when the priest consecrates it.) As a Protestant, I disagree with the doctrine of transubstantiation and do not believe this is what the Bible teaches regarding the nature of communion. On the other hand, my Roman Catholic friend beliefs it wholeheartedly.
During our conversation, my friend attempted to defend the idea that God could take on the form of material objects by pointing to Exodus 3 where he claimed that God actually took on the form of the burning bush when He spoke with Moses. If God can become a bush, why can't he become the bread and wine in communion? That was his line of reasoning. Our conversation went something like this:
Roman Catholic: In Exodus it says that God took on the form of a burning bush and spoke to Moses. If he could do that, why couldn't he become the bread and wine?
Me: Actually, Exodus 3 does not say that God literally became the burning bush. Verse 2 says, "The angel of the LORD appeared to him in a blazing fire from the midst of the bush." There is nothing in the text that says God became the bush. It wasn't necessary for God to do so in order to make His presence known "from the midst of the bush" and speak to Moses.
Roman Catholic: Well it doesn't say He didn't become the burning bush either! Where does it say that He didn't become the bush?
***Notice he has shifted the burden of proof.
Me: Wait a second. You are the one who brought this text up in support of your position. You are the one who made the original claim. Therefore, the burden of proof is on you to demonstrate that this text is saying what you are claiming it says.
Roman Catholic: But you are making a claim too! You are claiming God didn't become the bush! Show me where it says that!
***This conversation (can I call it ridiculous?) carried on for about half an hour.
Me: But as I mentioned, the burden of proof is on you since you made the claim. Whoever makes the claim bears the burden of proof. My only claim is that you have not made your case. You can't base your argument or evidence on what the text doesn't say. That is an argument from silence. Besides this, even if I grant that you are right on this point, it doesn't follow from this that transubstantiation is true.
Again, notice what happened here. First, my friend started out by making a truth claim, i.e. that God actually became the burning bush. I pointed out to him that there is no evidence or reason from the text to believe this.
Second, my friend attempted to shift the burden of proof to me by implying that it was not his duty to prove himself right but rather my job to prove him wrong!
In response to all of this, I pointed out three problems with his reasoning:
First, I rightly pointed out that, despite what he may think, the burden of proof rests with him. I tried to explain this to him as clearly as I could but in the end I don't think the information stuck.
Second, I pointed out that he was committing a logical fallacy: an argument from silence. Notice his statement above. During our conversation he implied that because the text does not say God didn't become the bush that this is somehow evidence that God did become the bush! The obvious problem with this fallacious reasoning is that you cannot base your argument or evidence on what the text doesn't say! That commits a logical fallacy, an argument from silence.
Third, I pointed out that even if he was correct in assuming God actually became the burning bush, it wouldn't follow from this that transubstantiation is true! Why not focus on more important passages in the New Testament that Roman Catholic apologists use to defend their views? Ultimately this was a silly conversation that got us nowhere.
First, never accept the burden of proof if it isn't yours to bear. Explain the rule "whoever makes the claim bears the burden." Of course, if you do make claims, be prepared to give reasons or arguments as to why you think you're right.
Second, don't get frustrated (as I did after a half hour of meaningless debate) when speaking with someone who seemingly is not willing to follow the basic rules of argumentation and logic. In cases such as this it is unlikely the conversation will ever be productive, or even get off the ground.
Third, explain yourself as best as possible. Stop, think for a moment, and pick your words carefully so you are able to speak as clearly and persuasively as possible.
Fourth, don't waste your time discussing issues that are distracting from the main topic. These are red herrings. Instead, focus in on the question under discussion and try to redirect the conversation toward more foundational and relevant matters.
Fifth, in the end, you may just have to "agree to disagree." If your interlocutor is refusing to be reasonable or abide by certain conversational rules it may be best to simply end the discussion on a friendly note and try again next time (if you dare).
(1) Greg Koukl, Tactics: A Game Plan for Discussing Your Christian Convictions, 59.