Koan Zen is a philosophical practice that bears a strong family resemblance to Wittgenstein's approach to philosophy. In this paper I hope to show that this resemblance is especially evident when we compare the Zen method of koan with Wittgenstein's suggestion, towards the end of his Tractatus, about what would constitute the only correct method in philosophy. Both koan Zen and Wittgenstein's method set limits to the reach of philosophical discourse. Each rules metaphysical speculation out of bounds. Neither, however, represents a rejection of the metaphysical. Where Wittgenstein enjoins silence in the face of the unsayable, a silence that allows the metaphysical to show itself, koan Zen calls for concrete demonstrations of that which cannot be captured in rational discourse. I attempt to illustrate this through discussion of a number of koans that serve as reminders that the philosopher (and Zen master) should say nothing except what can be said.