Why do you believe x?

I've just noticed this on Rosemary Grier's profile:

What reason do you have to believe the earth is flat?

What reason do we have to believe anything? Testimony. We're all biased. So's experimentation.

I've believed that for a good few years. The apostle John (with some help from Lesslie Newbigin) taught me it:

“I can do nothing on my own. As I hear, I judge, and my judgment is just, because I seek not my own will but the will of him who sent me. If I alone bear witness about myself, my testimony is not deemed true. There is another who bears witness about me, and I know that the testimony that he bears about me is true. You sent to John, and he has borne witness to the truth. Not that the testimony that I receive is from man, but I say these things so that you may be saved. He was a burning and shining lamp, and you were willing to rejoice for a while in his light. But the testimony that I have is greater than that of John. For the works that the Father has given me to accomplish, the very works that I am doing, bear witness about me that the Father has sent me. And the Father who sent me has himself borne witness about me. His voice you have never heard, his form you have never seen, and you do not have his word abiding in you, for you do not believe the one whom he has sent. You search the Scriptures because you think that in them you have eternal life; and it is they that bear witness about me, yet you refuse to come to me that you may have life. I do not receive glory from people. But I know that you do not have the love of God within you. I have come in my Father's name, and you do not receive me. If another comes in his own name, you will receive him. 44 How can you believe, when you receive glory from one another and do not seek the glory that comes from the only God? Do not think that I will accuse you to the Father. There is one who accuses you: Moses, on whom you have set your hope. If you believed Moses, you would believe me; for he wrote of me. But if you do not believe his writings, how will you believe my words?”

(John 5:30-47)

Within a few minutes of a conversation with a non-Christian it is obvious to everyone that you believe what you do (despite the questions) because you trust (ie have faith in) the testimony of the God who sent his Son to be nailed to a cross for your sins, and who has never been shown to be unfaithful. And it is clear to you at least that the non-Christian believes what they believe because they have trouble trusting anyone else's testimony all the way - let alone God's.

Doug Wilson has a story which says something similar.