Detail page for the cheat sheet. Legend: ✓ read · ◐ secondary/abstract · † unread · ✗ no source.
Introduction. Variety is a count of distinguishable states. Change the partition and the count changes, and with it the law’s verdict. The observer enters before the arithmetic.
Ashby says this himself
- 1956, §7/5, p. 125: “a set’s variety is not an intrinsic property of the set: the observer and his powers of discrimination may have to be specified if the variety is to be well defined” ✓ (read in the PDF on 22 Sept 2026). The example just before it is the semaphore: 64 arm positions, of which a distant observer can distinguish 36.
- The quote closes §7/5; §7/6 begins directly below it on the same page. The draft footnote cites §7/5 (corrected 22 Sept 2026).
- 1958: “If two observers differ in the distinctions they can make, then they will differ in their estimates of the variety” ✓.
- Consequence for the chapter: the partition problem is not a critic’s discovery. It is stated in the source and dropped in transmission, which is the same pattern as the stipulation and k.
Formal outside version. Siegenfeld & Bar-Yam (2025) make the dependence on coarse-graining explicit (see page 3) ✓.
One choice in three places
- Variety count: who distinguishes the states (this chapter).
- System boundary: what is inside and what is environment (Ch 5).
- Transducer: what a message keeps when it crosses a boundary (Ch 25).
- The Ulrich boundary questions (1983) are the normative side of the same point. The Stress Test paper §2.4 separates normative from constitutive boundary questions.
Attempts to measure variety in real organisations
- de Raadt, J. D. R. (1987). Ashby’s law of requisite variety: an empirical study. Cybernetics and Systems 18(6): 517–536. doi:10.1080/01969728708902152. Citation ✓; method †.
- Rosenkranz, C. & Holten, R. (2011). The variety engineering method. Information Systems and e-Business Management 9(1). doi:10.1007/s10257-010-0127-3. Title and journal ✓; content †. It is on the Stress Test reading list as the nearest existing thing to measuring variety on real information flows.
- Bertoni, V. B., Saurin, T. A. & Fogliatto, F. S. (2022). Law of requisite variety in practice. Safety Science 155: 105895. doi:10.1016/j.ssci.2022.105895 ◐. In an ICU, controller variety is a composite of network centrality, availability and reliability, and process variety is perceived task risk. It is a stated procedure, but it measures proxies, not counted states.
- Pfiffner, M. D. (2017). System viability of organizations and the aetiology of organizational crisis, PhD thesis, Utrecht. Items P.3 and P.4 ask whether ability to react, scope of action and range of offerings are “always sufficient to master expected” (then unexpected) challenges ✓ (read 14 Sept 2026). Nothing is counted. This carries the section “What the law becomes when someone has to measure it” and continues in Ch 18.
Importance for the chapter. Keep the claim narrow: we have found no documented case where two independent applications of a stated state-counting procedure to the same organisation produced comparable numbers. The law licenses arguments about possible arrangements, not figures.