The 'necessary/sufficient' framing of self-organized criticality's threshold is absent from the primary record — neither BTW's 1988 paper nor Bak's book uses that vocabulary, marking it a secondary-literature construct

self-organized-criticalitycomplex-systemsthresholdbak-tang-wiesenfeldnecessary-sufficientsource-disciplineprimary-source-verification

Read directly rather than through a secondary review, neither of the primary documents behind self-organized criticality frames thresholds using the words "necessary" or "sufficient." Bak, Tang & Wiesenfeld's 1988 companion paper (Phys. Rev. A 38, 364 — the longer paper to the 1987 letter) states the same no-tuning contrast Watkins et al. quote from the 1987 letter: an ordinary critical point "can be reached only by fine tuning a parameter (e.g., temperature)" and "so may occur only accidentally in nature," whereas the phenomena the paper studies are ones "where no fine tuning is needed." Read end to end, the paper's text contains no "sufficient" anywhere, and "necessary" only twice — both times in the procedural remark that in the self-averaging simulations "no resetting is necessary" (Secs. III B and III C), a statement about simulation method with no bearing on thresholds or tuning. Neither word ever appears about thresholds or about tuning. It states the no-tuning property as a flat, unqualified fact, never as one half of a necessary/sufficient pair. Bak's 1996 book (claim-bak-how-nature-works-independently-confirms-soc-no-tuning) uses "necessary" only for the non-SOC (tuned) case, never as a necessary/sufficient classification of thresholds within SOC.

The necessary/sufficient vocabulary is therefore a secondary-literature construct at every layer checked. It entered first as a Tier-3 MIT course project (Golyk 2012), which reported "necessary, but not sufficient" as a conclusion from renormalization-group analyses, not as BTW's words; and, independently and more rigorously, as the Tier-1 Watkins, Pruessner, Chapman, Crosby & Jensen (2015) review, whose own necessary ("phenotype") vs. sufficient ("genotype") split places thresholds only on the sufficient side (claim-soc-tier1-literature-places-threshold-among-sufficient-not-necessary-conditions) and treats their necessity as an open question (claim-soc-necessity-of-threshold-driven-interaction-remains-open-question). BTW themselves neither asserted, qualified, nor declined the framing — the question was always about the commentary, not about the primary.

This supplies the primary layer beneath claim-engineered-threshold-is-not-self-organized-criticality's correction history: the corrected reading (thresholds are sufficient, not shown necessary; BTW framed it neither way) now holds at the primary-source level and needs no revision elsewhere in the vault.