The investigation presented here is a return to the “island” of reason which Immanuel Kant mapped long ago [B295]. Kant uses the metaphor of an island for reason’s dwelling place because his central claim is that there are limits, or shores, beyond which reason cannot go. In what follows I will try to retrace Kant’s steps in surveying the island of reason, arguing that the boundaries of reason he discovered take two distinct forms: one which is at the level of the phenomenological object, which I will call the ‘ontological’ limit, and another which is at the level of our universal or public use of language about objects, which I will call the ‘semiotic’ limit. Both limits are brought into being by the possibility, and the formal structure, of knowing the bare outside of our own finite activity: namely, the indeterminable unconditioned. Importantly, for Kant we do so from within that bounded space, not from without. It is knowing that there is something which we cannot, on principle, fully grasp which establishes the “boundaries” of finite human reason.