Premise 4 is self-evident: to argue that humans CANNOT rationally infer knowledge claims is itself a rational inference — it's self-defeating. Some things are properly basic beliefs that don't require proof.

To deny premise 4 (that humans can rationally infer) requires doing the very thing you're denying. If someone says "I cannot rationally affirm knowledge claims" — that IS a rational knowledge claim. It's like saying "I cannot utter one single sentence in English" — self-referentially defeating. Winger and Stratton discuss Plantinga's concept of properly basic beliefs: some things (your own existence, the reality of the external world) are foundational and don't require philosophical proof. Philosophy should explain WHY we know things, not try to rebuild our very existence from scratch. "I exist" is obvious, intuitive, and the starting point — not something to be proven.