A gloss on first the section Paine quotes ( A758 B786)
1. Ignorance as motive, not paralysis
Kant begins by distinguishing types of ignorance. Some ignorance is contingent (we simply don’t know some facts yet), which motivates empirical or dogmatic investigation. But there is also necessary ignorance — ignorance grounded in the very conditions of our knowing — which is revealed only by critique. That’s the crucial distinction between simply bumping up against the limits of what we happen not to know, and recognizing the boundaries of possible cognition itself.
He stresses: ignorance known critically becomes a kind of knowledge — a “science” — whereas ignorance known only empirically is merely a vague awareness that there’s more out there than we presently grasp.
2. The sphere vs. plane metaphor
The extended image is helpful. If reason’s domain were like a flat surface with an indefinite horizon, we could never tell how far our knowing might reach — ignorance would always be open-ended. But if reason is like a sphere, then from any part of its curvature we can (at least in principle) work out the total extent and boundary.
The analogy is drawn from mathematics: by knowing the curvature of a degree of arc, you can infer the whole globe. Likewise, by analyzing the structure of synthetic a priori judgments, Kant claims we can infer the scope of reason itself — where it has jurisdiction and where it does not.
This is why his project is not mere “censorship” (Hume’s skeptical rejection of claims beyond experience), but critique: not simply banning speculative metaphysics, but charting the precise boundaries of possible cognition.
3. Hume as halfway point
Kant explicitly positions Hume as a “geographer of reason” who erred by thinking that because causality could not be justified
a priori, therefore no metaphysical principle could extend beyond experience. That’s skepticism as a resting place — useful for sobering us up from dogmatism, but not a permanent home. Kant’s third step is to give positive grounds for why certain
a priori principles (e.g. causality as a category) apply within experience but not beyond it.
This is Kant’s classic “Copernican” move: reason is not authorized to legislate beyond the field of possible experience, but within that field, it has real and demonstrable authority.
4. The architecture of the Critique
You can see Kant here making explicit the shape of the CPR as a whole. It’s not merely destructive of metaphysics, nor is it skeptical in Hume’s vein. Instead, it seeks to establish metaphysics as a science by:
- identifying the legitimate use of pure reason (within experience), and
- sharply delimiting the illegitimate transcendent use (questions about “objects” beyond possible experience).
Thus the “sphere of reason” is bounded, but not indeterminate.
5. Resonances
- The passage echoes Socratic docta ignorantia — knowing that one does not know, but in a disciplined and productive way.
- It also resonates with Buddhist cautions about “objectifying the non-objectifiable”: the distinction between what can be known under conditions of cognition versus what lies beyond them.
- It is one of Kant’s strongest rebuttals to both reductionism and naive empiricism: the critical path is neither endless accumulation of data (dogmatism) nor permanent suspension of judgment (skepticism), but systematic self-knowledge of reason itself.
A further reflection: - Kant addresses the limitations, not the limits, of knowledge. There may be no limit to the discovery of further empirical facts, but there are limitations inherent to reason itself, regardless of the accumulation of facts.
@Janus - this is typical of how Kant says there is a 'determinable fact of the matter'. It relies on sophisticated arguments to be sure, but that is what he is claiming.