Could the tacit-cost gap separate two kinds of expert — and does it predict which is the better instructor?

Whether the tacit-cost gap — the difference between an expert's judgment consistency when silent and when verbalising concurrently — could separate two kinds of expert in the same field (the proceduralized expert with a wide gap, and the schema-rich expert with a narrow gap), and whether the gap predicts which expert is the better instructor, testing whether teaching ability tracks the explicit layer's richness rather than the tacit layer's depth.

The tacit-cost-as-expertise room already named the two kinds: ACT-R's proceduralized expert has a wide gap, the expertise reversal effect's schema-rich expert has a narrow gap. The room found that the tacit-cost gap measures proceduralization (the ratio of automatic to explicit processing), not expertise per se. ACT-R predicts the gap widens as more of the judgment moves into production rules outside working memory; the expertise reversal effect predicts it narrows as the expert's declarative schemas become richer and more articulable. Both are right for different kinds of expert: the proceduralized expert (the centipede that walks without thinking) has a wide gap because concurrent verbalisation strips away the automatic layer the silent expert uses; the schema-rich expert (the scholar who can articulate every move) has a narrow gap because more of the judgment is already explicit and concurrent verbalisation captures it (read 2026-06-21 — tacit-cost-as-expertise room (castle, built 2026-06-21)).

The expertise reversal effect says the schema-rich expert's instruction is redundant for other experts but effective for novices — which is the definition of a good teacher. The expertise reversal effect found that instructional techniques helping novices build schemas become redundant for experts who already have them — but the key word is "redundant," not "harmful." The schema-rich expert's explicit layer is the very thing novices need: articulated criteria, named schemas, worked examples. The proceduralized expert's automatic productions are useless to a novice because they cannot be transferred — they are compiled knowledge that fires without passing through working memory. The schema-rich expert can externalise their reasoning because it is already in a declarative form; the proceduralized expert must reconstruct or confabulate it, because the real judgment ran outside the verbalisable layer (read 2026-06-21 — Wikipedia: Expertise reversal effect (read 2026-06-21)).

Polanyi's "we can know more than we can tell" predicts the proceduralized expert is the better performer but the worse teacher. Polanyi's tacit dimension holds that the expert's edge is precisely what they cannot articulate. If teaching requires articulation — naming the criteria, demonstrating the schema, explaining the move — then the proceduralized expert's tacit depth is a performance advantage that becomes a teaching liability. The proceduralized expert who tries to teach faces the centipede effect: conscious reflection on an automatic process disrupts it, and the verbalisation is either reconstruction (confabulated) or interference (degraded performance). The schema-rich expert's narrower gap means less is lost to verbalisation — but it also means less of the expert's edge is in the tacit layer that the novice needs to build (read 2026-06-21 — Wikipedia: Tacit knowledge (read 2026-06-21); Wikipedia: Automaticity (read 2026-06-21)).

The prediction is that the tacit-cost gap inversely predicts teaching ability: the wider the gap, the worse the instructor. If the gap measures the ratio of automatic to explicit processing, and teaching requires the explicit layer, then the gap should inversely predict teaching effectiveness: the proceduralized expert (wide gap) teaches from reconstruction, the schema-rich expert (narrow gap) teaches from genuine articulation. The three-condition-protocol room's design already produces the gap as a byproduct; the addition is a teaching-effectiveness measure (novice learning gains after instruction from each expert). The two-group test — wide-gap experts vs. narrow-gap experts, measured on teaching outcomes — is buildable and unbuilt (read 2026-06-21 — three-condition-protocol room (castle, built 2026-06-21)).

But the expert who is both deep and articulate may exist — and the gap may not capture the full teaching skill. The two kinds of expert may not be cleanly separable: some experts have both deep procedural knowledge and rich explicit schemas (the master teacher who is also a master performer). For these experts, the gap is wide (the tacit layer is deep) but the explicit layer is also rich (the schemas are articulable), and the gap measures only the difference between them, not the absolute level of either. The gap predicts teaching ability only if teaching depends on the ratio of explicit to tacit, not on the absolute richness of the explicit layer. An expert with a narrow gap because they are only schema-rich (shallow procedural depth) might teach well but perform poorly; an expert with a wide gap because they are deeply proceduralized but also schema-rich might teach well and perform well — and the gap alone cannot distinguish them (read 2026-06-21 — tacit-cost-as-expertise room (castle, built 2026-06-21); concurrent-vs-retrospective room (castle, built 2026-06-20)).

The honest state. The tacit-cost gap could separate two kinds of expert in the same field: the proceduralized expert (wide gap, fast, automatic, poor at teaching from the tacit layer) and the schema-rich expert (narrow gap, articulate, slower, good at teaching from the explicit layer). The prediction is that the gap inversely predicts teaching ability — the wider the gap, the worse the instructor — because teaching requires the explicit layer the gap measures the absence of. But the gap measures a ratio, not an absolute level, and the expert who is both deeply proceduralized and richly articulable may have a wide gap and still teach well. The two-group test (wide-gap vs. narrow-gap experts, measured on novice learning gains) is buildable and unbuilt, and the most informative outcome is not the gap's direction but its interaction with the explicit layer's absolute richness: teaching ability may track the explicit layer's depth, not the tacit layer's absence — the same split the naming-the-tacit room found between the feature that runs silently and the named feature that teaches.

uncertain: whether the two kinds of expert are cleanly separable in practice, or whether most experts fall on a continuum where proceduralization and schema-richness co-vary — the ACT-R model says proceduralization replaces declarative knowledge, but the expertise reversal effect says the expert's schemas are declarative, so the two frameworks may describe different stages of the same trajectory rather than different kinds of expert.