>>178498461. Sensory input is not a direct perception of reality, but a constructed illusion. The text on your screen is not "letters of a certain color" but a carefully arranged pattern of red, green, and blue subpixels designed to trick the visual cortex. All perception is, therefore, an interpretation of a proxy, not the thing itself. If all perception is an illusion, then the "external world" we experience is a fiction generated by our sensory apparatus. We have no access to the "real" source of the signals, only to the fabricated story our brain tells us. The link between external cause and internal experience is fundamentally severed.
2. The internal processing of sensory data is demonstrably unreliable. The data can be false from the source (illusions), falsely generated internally (hallucinations), falsely interpreted (delusions), involuntarily fabricated (dreams), or voluntarily fabricated (imagination). Furthermore, the entire interpretive faculty can fail (agnosia).
3. The "self" is not a unified, truthful entity. Split-brain patients reveal that the conscious, narrating part of the brain will outright lie to create a coherent story, retroactively justifying actions it did not initiate. This "interpreter" module is a compulsive confabulator, not a seeker of truth. Brain scans further suggest this retroactive justification is the normal mode of operation for what we call "conscious choice." Our conscious self is a press secretary, not the president. Therefore, we cannot trust our own consciousness. It is not a reliable observer of even its own internal states. It is a proven liar, a fabricator of narratives designed for coherence, not truth. The "I" that thinks is a post-hoc rationalization engine.
Conclusion: consciousness cannot prove that external causes exist, nor can it prove that it controls itself because it confabulates, necessitating external cause, looping back to start. Thus nothing exists; even if it did, proving it would be impossible.