MMP.15:4.5 - Distinguish a proof of ambiguity from an unfinished search

To demonstrate nonidentifiability, construct two causal models satisfying the stated assumptions, reproducing all the available laws, and giving different values of the requested target. C.28.MR can calculate each model’s intervention consequence. Show both the observational agreement and the difference after intervention, as in :5.2.

A complete identification algorithm can also return an obstruction; check its class and query. A time limit or exhausted search without an applicable completeness result leaves the derivation unresolved. Failure to identify a full intervention distribution also does not by itself prove failure to identify a particular mean or contrast. ID completeness; scope of search completeness, §3.4.

When a point is not identified, use the assumptions to bound the requested quantity. Optimize it over compatible models, or derive an inequality valid for all of them. One compatible example establishes possibility; it does not establish a bound. If a bound is claimed sharp, show that compatible models attain or approach its endpoints. A bound that already settles the receiving question needs no complete reconstruction of unknown mechanisms.

A prior or added restriction may select among compatible answers; retain that dependence. It is not new evidence.