Defining beliefs

Most of us can defend what we believe using the Bible, but can we define what we believe using the Bible? Sounds like a strange question, but what I have noticed is that there are many differing beliefs being presented and defended, but very few being clearly defined by the Bible. For example, and this is just an example with the discussion to be saved for a later blog, is there a clear definition for the Trinity in the Bible? Note, I am not asking for the evidence to support the concept of a Trinity. I am asking for a definition.
I have found some interesting discussions in support of and against the Trinity. Both sides use the Bible to defend their position. Can two opposing views be right?
Another example, creation and evolution. Young earth vs old earth. This is a little harder, since the evidence is not only found in the Bible, but there is also physical evidence available to be examined. Aside from the evidence, what would cause someone to believe in creation vs evolution or a young earth vs and old earth.
Okay, okay, now I am getting into issues of faith, yet another future blog topic...