Man, unlike all other creatures, can relate to the world as a unity. His experience is of a 'world,' meaning all things are seen as part of a unified whole. Since man can understand reality as one thing, he will, as a searcher of causes, seek to explain the world not merely with respect to all of its individual constituents but also as a unity. This is not a mere aspiration, this is something that men naturally seek to do.
In a way, the post-modern turn is a decisive rejection of this notion, it is an affirmation of the idea that reality is really a set of essentially unrelated elements, and the vain quest for a unified explanation necessarily does violence to the irreducible differences found in the world. This can be true, but only if our principles are not, in fact, the proper first principles of unity. In other words, the skepticism of post-modernity is not the humble recognition that the world cannot be understood in its most fundamental mode, but rather that the modes of our recent analyses have been inadequate.
If we seek to reduce the world to a mathematical model, or a physico-mathematical model, we must end in skepticism because these are not the principles of unity. The unity of the world is metaphysical, and the proper object of metaphysics is that which truly gives unity to our experience. It is being.