Lesson 3 built a production system from IF–THEN rules over a working memory of facts. ACT-R (Adaptive Control of Thought—Rational) is what happens when that skeleton grows into a full theory of human cognition, built by John Anderson starting in the 1980s — and its first big move is splitting memory into two kinds that lesson 3 left undifferentiated:
- Declarative memory — “knowing that”: facts, retrievable as chunks. A chunk is a small, structured unit of knowledge (think: a record with a few named fields) — “the capital of France is Paris,” “the knight on d5 is pinned,” “my opponent is rated 2400.” Chunks are things you can state.
- Procedural memory — “knowing how”: production rules, exactly lesson 3’s IF–THEN form, that fire on the contents of declarative memory (and the current goal) to produce behavior. Productions aren’t things you consciously state — you can’t fully narrate the rule that lets an experienced driver brake at the right instant; you just do it.
Every chunk in declarative memory carries an activation value — a number capturing how easily and quickly it can be retrieved right now. High-activation chunks surface fast and reliably; low-activation ones are slow, error-prone, or simply fail to come to mind. (This is lesson 2’s “chunk” — Miller’s 7±2 — made formal and numeric: a unit worth holding onto, now with a quantity attached to how held-onto it is.)
A chess player’s mind holds all four items above. Which one lives in procedural memory rather than declarative?