What is extended mind thesis?

Extended mind thesis is a concept in personal epistemology: Writing does not record thinking. Writing IS thinking. The act of externalization transforms a vague internal sense into something precise enough to inspect, challenge, and build on.

Example: Two engineers argue about system architecture for 30 minutes. Neither is wrong — they're solving different problems they haven't made visible. The moment someone draws both mental models on a whiteboard, the misalignment becomes obvious in seconds. The diagram didn't add information. It forced precision that revealed what was already there.

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.