Though this conclusion that our reason is confined within the borders of our experience, and that reality in itself is permanently screened off from us by our own sensory limitations, may seem to some to be a very outlandish idea; in fact it is at the very center of Western philosophy. In perhaps the most famous metaphor in Western thought, Plato likened human beings to people living in a cave, shut out from the light of the sun, seeing only shadows and mistaking them for reality. Plato regarded our perceptions as mere images of a deeper and higher reality, the so-called Platonic forms, that he located somewhere outside the realm of human experience. And Plato's teacher, Socrates, regarded himself as the wisest man in Athens because he alone knew how little he knew. For all his breathtaking originality, Kant is squarely in the mainstream of Western thought.
D'Souza describes the beginning of Plato's allegory of the cave, but leaves out the second half. In Plato's story, one of the men chained in the cave is released and is able to make his way outside the cave, experience the sun, and see reality as it is. This process is, of course, the allegory of philosophy. The ordinary man is trapped within the conventional understanding of things (that is, common opinion); the philosopher is the man who, through philosophy, is able to transcend convention and understand reality as it is. If we are to interpret Plato's cave in terms of Kant, then we need to remove any hope that the man in chains is able to escape. Instead of philosophy arising when the man escapes his chains, it occurs when the possibility of his predicament occurs to him. He begins to distrust his naive deductions from his phenomenal experience and invents the critical philosophy. While he can never escape his chains, he has gained the only liberation possible to him: An understanding of his position and release from his prior false beliefs. He can never know reality as it is, but no longer does he labor under illusion.
The liberation Kant provides is superficially similar to that of Socrates, but they are radically different. Socrates's ignorance is subjective; he knows that he knows nothing, but he does not pretend to know that no one else knows anything, and even less, that no else can know anything. The Socratic conclusion is a beginning to philosophy; realizing that all his prior opinions were poorly founded, the Socratic philosopher is spurred to search for true wisdom. The Kantian conclusion is an end to philosophy, classically understood. The philosopher realizes that his prison is his own nature and is inescapable; he universalizes this conclusion to the point that no one else can or ever will know anything (about reality as it is, of course). The philosopher's task from thenceforward is not to search for true knowledge of reality (since he has concluded it is impossible), but to help his fellow men by bringing them to what truth is available to us: The truth provided by the critical philosophy that exposes the Socratic quest for the fool's errand it is.