Fishbone / Ishikawa Diagram

Origin. Ishikawa Kaoru, Kawasaki shipyards, 1960s.

Mechanism. Partitions causal space into fixed categories before searching within them, which prevents the search from converging on the first plausible cause. The categories are a covering, not a theory.

Procedure. Effect at the spine. Ribs by category: 6M for manufacturing (machine, method, material, manpower, measurement, milieu) or 8P for service. Branch each rib until the causes are testable. Then test, ranked by cheapness of the test.

Applies to. Multi-causal failures; team diagnosis where the aim is coverage.

Limitations. Produces a taxonomy of hypotheses and no evidence. It is the beginning of diagnosis, and it is routinely treated as the end of it.