There has been a lot of discussion lately surrounding postmodernism and Christianity. My friend Scott Simmons recently provided me an excellent explanation from which the following heavily borrows:
Modernists argue that all Truth can be proven either rhetorically or empirically. This led to the scientific revolution, among other things. The problem is that in science, as in so many fields, we learned time and time again that we were constrained by a host of imperfections, whether they be incomplete information, imprecise methods, statistical issues, et cetera. Of course, modernists argue that this can simply be resolved with better mechanisms, i.e. we develop a better telescope and see more stars, it doesn’t mean that they weren’t there before, it just means that our equipment was insufficient to see them.
Postmodernists argue that truth cannot be perfectly derived rhetorically or empirically. That is to say that there is always a space of the unknown that breaks the continuity between rhetorical or empirical evidence and ultimate Truth. Secular postmodernists thus conclude that to say x is true is more a matter of personal understanding, values, or faith rather than in fact offering ultimate Truth.
Perhaps a chart would demonstrate better:

Science would say that all the evidence points to the truth being the green line. A philosopher might point to truth being the blue line. But in fact Truth or reality might be the red line. Given the simple fact that no one knows what happens in the area of the unknown, anything can happen and thus truth is subjective.
Of course, everyone continues to argue that their truth is in fact Truth from the philosophers, to the scientists, to the theologians, to the outright crazy. Many secular postmodernist take this an additional step to say that truth is solely based in perception and thus there is no ultimate Truth. This is where Christian postmodernists differ.
Christian postmodernists believe that there is in fact an ultimate Truth and, though it may be hinted at and pointed towards in science, philosophy, and religion, it is the sole dominion of God. That is to say that human understanding of Truth lacks perfection and by very definition remains always deficient from ultimate Truth, always in need of redemption, and always requiring faith.
All Christian efforts to prove God, whether scientific, philosophical, or theological have and always will fall short. Wonderfully, this simply not only affirms the requirement of faith, but the core and ultimate need we all have for God!
Providentially, Christians worship a God who speaks. The one true God who has chosen to share ultimate Truth with all of mankind through His Word, through the Holy Spirit, and through His Son. Our understanding remains deficient and must always be examined and challenged, but we get to experience ultimate Truth, here and now, like no other people and in eternity, in perfection.
Soli gloria Deo.