Heuer's ACH eliminates hypotheses by scoring each evidence item against every competing hypothesis in a flat matrix, not by chaining rule premises

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In Richards J. Heuer Jr.'s Analysis of Competing Hypotheses, the analyst first enumerates the complete set of competing hypotheses up front, then — in Heuer's own words — "creates a matrix with hypotheses listed across the top and evidence listed down the side." The matrix is worked one evidence row at a time: for each item of evidence the analyst asks, of every hypothesis, whether that hypothesis being true would make the item likely to be seen. Elimination is a tally over the whole matrix — the hypothesis with the most inconsistent evidence is the weakest — following "the fundamental precept of the scientific method that one should proceed by rejecting or eliminating hypotheses, while tentatively accepting only those hypotheses that cannot be refuted" (claim-ach-step-5-instructs-analysts-to-disprove-not-prove).

There is no rule base, no conclusion-indexed retrieval, and no recursive subgoaling for missing facts. The structure is a single flat evidence-by-hypothesis grid, not a chain of antecedents resolving to subgoals. This sharpens — with a fresh quote and sha — the mechanism behind Heuer's own account of ACH's foundations, which the vault already cites from the same 2007 primary.

One scope note on the procedure, because it is easy to overstate: the matrix is scanned row by row (one evidence item across all hypotheses, then the next row), not evaluated all at once. ACH is exhaustive — every cell is eventually scored — but Heuer's text describes a sequential pass, not a parallel or simultaneous evaluation. The contrast that matters is with backward chaining's goal-directed recursion, not a claim that ACH computes the whole grid in one step; see observation-ach-backward-chaining-mechanism-comparison-is-false-friend and the long-standing finding that no source documents the two being compared.