This is the second post in the first section in my series, theology in bullet points. (Here are three of the later sections that I've already done).
"All truth is God's truth," the saying goes.
1. The basic idea of this saying is that, if something is true, then it not only fits with God, but it comes from God, since God designed and created all things. You might say that the Truth is everything that God believes or, rather, that God knows. You might say that the Truth is everything God has created to be true in this universe. 
It is in the application of the saying that Christians begin to get bent out of shape. This saying is usually used to say that if science comes up with something as a truth, then that truth fits with God just as much as a truth from the Bible, since "all truth is God's truth." Someone might then object that the Bible gives us a much more certain view of truth than science or some other field like psychology.
So while everyone mostly agrees that truth is truth, wherever you may find it, arguments over this saying amount to disagreement over where and how you find that truth. Here we enter into debates over whether truth is mostly something that we can discover or whether truth is mostly something that is revealed. The saying, "All truth is God's truth," is usually made by someone who is arguing that the truths that are discovered are just as much truths as the truths that are revealed.
There are several possibilities: 1) human thinking is fallen or damaged such that we cannot hope to reason or discover our way to truth; 2) human thinking is perfectly reliable at arriving at the truth by reason or discovery; 3) there are some truths at which human reason and discovery can arrive but others where we will never come up with the right answer without direct revelation from God.
Here we might pause to notice that we are thinking. We cannot have this discussion without thinking. Indeed, we cannot interpret the Bible without thinking. True, the Spirit might zap you with a direct revelation while you are reading it. But any attempt to understand the Bible can only take place with the involvement of basic reasoning. This is a fundamental insight.
Therefore, reason is more fundamental to the process of arriving at truth than the Bible can be, because the Bible itself is an object of knowledge. The Bible contains definitive truths, but you cannot know them apart from the exercise of basic human reasoning. The Bible provides true content, but it does not provide the most fundamental mechanisms by which my mind organizes that content, which have to do with the "operating system" we call, "thinking."
Nor does the Bible exhaust the Truth. The Truth is a much bigger set with many more elements than the Bible. The Bible does not give the birth date of my grandfather. It is a truth that is not in the Bible.
2. The bottom line is the proper mix of presupposition and evidentiary thinking. To what extent should we allow evidence to trump our presuppositions or to what extent should we let our presuppositions steer our processing of evidence?
Presuppositions are things that we assume without evidence. Those who most favor a presuppositional approach are quick to point out that we all have presuppositions--often ones that we are not even aware of. If you ever took a geometry class, you might remember that you started with axioms and postulates like, "For every two points A and B, there exists one and only one line that contains them both." You cannot prove this. It is a matter of definition. Then you built "theorems" out of these basic assumptions.
However, those who most favor a presuppositional approach usually go well beyond common sense assumptions like these. A presuppositional approach usually wants you to assume entire ideological systems and shove them down the throat of reality no matter what evidence you might find to the contrary. The fundamental problem is the source of such systems. They usually claim to be biblical, but this claim proves to be mistaken and self-contradictory.
For example, it is impossible for any such "worldview" to be truly biblical because the Bible was not written as a worldview textbook. The books of the Bible themselves tell us that they were written to specific audiences at specific times and places to accomplish specific purposes. Any attempt to abstract a philosophical worldview from them thus involves a massive exercise of reason, inference, and induction in a way that stands in tension with the obvious genres of the documents themselves. 
In the end, such attempts are pre-modern, based upon unreflective readings of the texts themselves. Ideological presuppositionalism has to make massive assumptions about the biblical texts in order to get any content for its assumptions from the biblical texts. In other words, its most basic assumptions still come from outside the biblical texts, assumptions about how to draw information from the biblical texts.
Such interpretation obviously involves fundamental reasoning processes on a massive scale. Thus, the presuppositional approach on this level is fundamentally incoherent. It must base its presuppositions on massive amounts of thinking and reason while claiming to by-pass such reasoning as a source of truth.
3. We cannot escape evidence. There is a certain personality that can dig a hole of ideological coping mechanism that is as profound and complex as it is perverse. But there is a point where most if not all human minds will finally concede what lies before my eyes. I may not want my father to be dead. Maybe that was not really his body at the funeral. Maybe he has just gone on an extended trip. Maybe he was abducted by aliens.
But eventually, the evidence may persuade me. Evidence almost never proves something. Except for my belief that something exists, all other conclusions about the outside world require some degree of faith. I do not think that I am dreaming right now or in a computer program. I cannot prove it, but it is reasonable to think otherwise. I am willing to take it on faith.
Evidence can be misleading. My senses can be misleading. I can make mistakes in my reasoning. Evidence is not an infallible indicator of truth. Science can go for long periods of time with models and paradigms that are rejected in the end.
Nevertheless, it seems reasonable to believe that God is not a trickster, that the evidence of the universe more or less points us in the right direction. "There is something up in the sky," is much more reasonable than, "The Devil tricked me into thinking that there was a shiny ball above my head today."
4. The point is that we can find truth not only in the Bible, but in science and in the world around us. Our apprehension of that truth will always face the potential skew of my thinking and reasoning, not to mention the fact that I can only see the universe from one small, tiny spot within it.
We call the truth that we find in the Bible and in God's direct revelations to humanity, special revelation. Then we call the truths that anyone can discover in the world, natural revelation. I strongly believe in both. Truth is both revealed and discovered in the world.
All truth is God's truth, wherever we may find it. We can find it in the Bible, but we can also find it as we behold the glory of the heavens (Ps. 19:1-6).
Next week: God has revealed himself in nature.
 At this point someone might say that Jesus is the "way, the truth, and the life" (John 14:6). Certainly this is true, but it is a metonymic statement. That is, truth is so associated with Jesus, that we can figuratively say that he is the truth.
A metonymy is a figure of speech where we call something by the name of something closely associated with it. Let's say I always wear a particularly goofy hat. So you might say, "Here comes the hat." The hat is so closely associated with me that you can say that I am the hat.
To say "God is love" or "Jesus is truth" is to use a metonymic figure of this sort. It is to call God by a characteristic that dominates his nature. It is to call Jesus by something to which he is key. It is not to say that if you were to look at the atoms of God or Jesus under a microscope you would conclude, "Well, what do you know? God's atoms are made up of love!" Or, "Jesus' cells really are made up of truth."
So to believe in Jesus is to understand the most significant aspects of the universe. But every truth is not covered by the category of Jesus. "There is a trampoline in the backyard" may be a true statement, but it is not a statement about Jesus in any obvious or straightforward way. (At this point, someone will no doubt try to come up with some tortured and convoluted connection)
Jesus is part of the Truth, just like the Bible is part of the Truth. However, neither exhaust the Truth. To say otherwise is to be confused about what a statement like, "I am the truth" means.
 The degree of defensive backpedaling that can take place in argument is nothing short of astounding. "God has to define what the appropriate definition of a genre is." OK, and how do you know what that definition is? Did God tell you this morning? You can't answer, "the Bible," because we are talking about how to interpret the Bible. You cannot get an answer on that question from the Bible until we know how to get an answer from the Bible.
The level of irrationality to which some will go to defend an obviously incoherent position is nothing short of astounding.