Authority

I'm sure most of my loyal readers have given up on me every posting anything again. Well, I'm in the middle of final exams, so I don't have enough time to think about things to post. I was mulling over a thought that's haunted me for a few years. I'd like anyone who reads this to post an answer to the question:

"How can a protestant know what Biblical truth is?"

I really would like to know what you think. If you're reading this and you post an answer, get some of your friends to post answers also. Thanks.