What is mental inventory?

Mental inventory is a concept in personal epistemology: Your sense of cognitive completeness is an illusion. What you can access at any moment is a context-dependent sample of what you actually know — and the sample changes without your awareness.

Example: Ask yourself to list every active commitment you have right now. You'll produce a list that feels fairly complete. It's missing at least 30-40% of the actual items. The items aren't gone — they're in long-term memory — but they're not in your current retrieval set. What's worse: you don't feel the gap. The list feels complete because your brain treats available information as all information.

This concept is part of Phase 1 (Perception and Externalization) in the How to Think curriculum, which builds the epistemic infrastructure for perception and externalization.