Rules of Thumb and Adaptive Rationality


Rules of Thumb and Adaptive Rationality

Human cultures have used rules of thumb for centuries. During the past century, however, they have been vilified to near extinction. Is their demise justified? Roope Kaaronen

Photo by Adam Rhodes

Author: Roope Kaaronen

Affiliation: Postdoctoral researcher, University of Helsinki

Rules of thumb are simple and practical cognitive shortcuts that make use of bodily and environmental features. Human cultures have used rules of thumb for centuries to guide agriculture, technological development, and other aspects of social life. During the past century, however, rules of thumb have been vilified to near extinction. Is their demise justified?

Frederick Winslow Taylor was on a mission—to replace traditional rule of thumb methods with scientific and standardized procedures. Following the rapid industrialization in the 19th century United States, a bottleneck in factory workflows had appeared that was all too obvious to Taylor. The unique, mnemonic, and idiosyncratic working methods of each artisan, engineer, or craftsman were incompatible with the modern factory operations that demanded scientific precision, timeliness, and predictable outcomes. Local artisanal traditions were not fit for the emerging modes of global mass production.

Taylor’s industrial philosophy came to be known as Taylorism. One key aspect of Taylorist principles1 quoting Taylor himself, was to do away with “inefficient rule-of-thumb methods,” which were “still almost universal in all trades,” and in practicing which workmen “wasted a large part of their effort.” An effective industry, Taylor asserted, would have standardized workflows, guaranteed outcomes, and optimized divisions of labor. Notably, Taylorism caught the eye of communist and capitalist regimes alike: both were determined in the quest for what James C. Scott calls high modernism2 where locally adapted knowledge would gradually be replaced with universally applicable standards and scientific guidelines.

For traditional rule of thumb methods, this was only the beginning of their misery. The vigor for thinking in terms of standardization, optimization and rationalization swept through the industrial world in the early 20th century, and soon found its way into the human and social sciences. First, unsurprisingly, this happened in the more established field of economics. But later, the standardization ethos found its way to our minds, as well, taking over the nascent fields of psychology and cognitive science. The cognitive revolution, as it came to be known, sought to discover the “laws” of how the mind, and its contents, operate. Its driving motives were to measure cognitive aspects such as intelligence and reasoning in terms of standardizable terminology—bell-curves and universal diagnostics. The upshot was that practically anything that deviated from the standardized, optimized, textbook “rational man” would be denigrated as invalid, malfunctional, or biased.

And so, rules of thumb received another blow. This time they were denigrated in the field of behavioral economics, where rules of thumb were discussed interchangeably with “heuristics”. Heuristics, these authors argued3 were intuitive rule of thumb methods that people often resort to, but which regardless often led our minds astray and to suboptimal decisions. Eventually, a range of public policies ensued, led by fervent social scientists—the Nudge4 advocates—who took on their quest to help citizens overcome their heuristics and biases.

Altogether, it seems fair to say that rules of thumb have got a bad rap during the past century. Recently, however, critics have pointed out this isn’t entirely justified. Researchers in the new fields of ecological5 and adaptive rationality6 have highlighted that often, in everyday environments, good judgments do not require complex cognitions7 and in appropriate contexts, rules of thumb may prove to be particularly adaptive. As Herbert A. Simon once wrote8 rationality should be thought of as a pair of scissors, where one blade represents the mind and the other the structures of the environment. Only when both are in place is the mind’s cutting edge sharp. Instead of dismissing rules of thumb altogether, we should focus on context, studying rules of thumb in the local environments they have adapted to operate in.

Curiously, very little work has been done in the way of uncovering how rules of thumb have guided human cognition, adaptation, and cultural evolution in our everyday environments. If rule of thumb methods truly were so terrible, why would they have evolved in so many cultures to begin with? In a recent research article, we sought to address these questions.9

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Rules of thumb have been indispensable in technological evolution. Exemplary cases are found in Yup’ik traditions in kayak construction, around the region that is now southwestern Alaska. A seaworthy kayak is one that has stability, but not at the expense of maneuverability. It is responsive and feels as if it were at one with the paddler. A kayaker myself, I tend to think of the tip of the bow of the kayak as an extended sensory organ, a feeler that gathers information from the waters and resonates through the kayak’s hull to my feet and torso. This requires near-perfect fit with the kayak. Because humans come in variable weights and dimensions, no universal, mass-producible, or standardized fit is suitable for all paddlers. During centuries, even millennia, of kayak construction, traditional knowledge has evolved convenient rules of thumb methods to adjust for this variation.

How this is achieved is hinted in the very name of the concept, “rule of thumb”. Traditionally, many artisanal groups have used embodied units such as the thumb-width or thumb-length as rough but useful measures. In Yup’ik kayaking tradition, various other bodily ratios10 are utilized. These are conceptualized by the Yup’ik, in an exemplary case of embodied cognition11:

  • Yagneq: the length of outstretched arms from fingertips (the arm span).
  • Tallim cuqii: the length from extended fist to armpit.
  • Taluyaneq: the length from middle of the torso to the end of fingertips.
  • Ikuyegarnerek malruk: the distance of two elbow lengths made by placing one’s fists together.
  • Ikuyegarnereq: the length from the elbow to the end of the fist.

As a rule of thumb then, a kayak would be two Yagneq plus one Tallim cuqii and one Taluyaneq long. This includes the length of the cockpit, which is one Tallim cuqii. The height of the kayak would be one Ikuyegarnereq, and the width at the cockpit one Ikuyegarnerek malruk. The use of measures like these would ensure that each kayak is custom-tailored to the bodily dimensions of the individual kayaker who would paddle it. No such tailored fit could be achieved as conveniently by using standardized—or, excuse the pun, Taylor-fit—units of measure.

Next, consider how rules of thumb allow humans to think with their environments. Most, if not all, traditional cultures around the globe make use of traditional ecological knowledge, and particularly, phenological knowledge. Phenology refers to the study of periodic or seasonal events in biological life cycles. Phenological knowledge, in turn, makes use of these recurrent ecological events for human ends. Typically, this involves using the appearance of one bioindicator (e.g., a bird or a flower) as a simple rule to infer the presence of another ecological event.

Take, for instance, the Nlaka’pamux people12 around what is now British Columbia, who use the blooming of the wild rose as a signal to indicate that soapberries are ready for harvest, or the leafing of desert currant to signal that the steelhead trout are running in a local river. In my home country, Finland, traditional knowledge of this kind is common: as a rough rule of thumb, the planting of flax is timed with the flowering of the bird cherry. Birchbark, which is used for tinder and crafts, is best removed from a growing tree during the bloom of rye.

There is an obvious advantage to thinking with environments instead of relying on standardized calendars, such as the Gregorian calendar. Since each year varies considerably from the other in its weather and temperature patterns, one cannot reliably assume that a cultivar should be sown on a specific day on a specific month. Instead, by utilizing reliable local bioindicators, such as the blooming of a flower, one can gain affirmation from the environment that the growing conditions (temperature, humidity, etc.) are at least within a satisfactory range.

Rules of thumb have also been used in traditional architecture, and have been important cognitive tools in guiding the ways in which we construct our ecological niche.13 The architects of the past were often not mathematically or scientifically trained, and instead relied on simpler but effective forms of knowledge that afforded the construction of even complex structures, such as the Gothic masterpiece, the cathedral of Chartres. In wonderful work of cognitive archaeology, John James14 has uncovered the various rules of thumb the several generations of architects used to build Chartres. In many cases, it turns out that the architects of the time did not even have universally accepted measures of the “foot”, and instead relied on subjective foot-lengths. Yet still, they managed in designing and constructing one of the most awe-inspiring buildings in existence.

This issue of The Side View focuses specifically on the work of architect Christopher Alexander, whom many consider a luminary figure in the art of thinking with environments. Perhaps it is little surprise, then, to find that Alexander too founds his work on a variety of rules of thumb. Consider, for example, the following rules from The Pattern Language:15 “Balconies and porches that are less than six feet deep are hardly ever used,” and "When they have a choice, people will always gravitate to those rooms that have light on two sides.”

In our research, we identify many further rules of thumb that have guided social cooperation, ancient legal codes, religions, the design of historical technologies, and foraging strategies16. Generally, rules of thumb were far from ineffective, and had adapted to solve local challenges in idiosyncratic and cognitively efficient means. Rules of thumb served as simple scaffoldings on top of which more complex and elaborate cultural structures could emerge.

So, what it is that makes rules of thumb so adaptive? First, rules of thumb are easy to learn, memorize, and teach. Thinking about a kayak’s length in terms of arm spans is much more convenient than memorizing the variable lengths in universal units such as inches or centimeters. Rules of thumb are therefore easily embedded into mnemonics, stories, and analogies—some of the key drivers of human cognition and cultural evolution.17 Second, rules of thumb offload18 much of cognitive processing (e.g., memorizing and calculating) to the body and the external environment. Using reliable cues and measures such as blooming flowers or thumb-widths as guides for behaviors may simply be more efficient than thinking in more complex manners. Third, good rules of thumb are almost always embedded in local knowledge, context, and tradition: they make use of the kinds of local events and features that standardized procedures may overlook. And finally, rules-of-thumb are often user-specific and allow for personal variation in how they are used and applied. This is especially important in cases where no one-size-fits-all solutions exist, such as in kayak construction and many other practical crafts.

It was only a century ago when Taylor’s mission to replace rules of thumb took flight, but it is already turning out to be a blunder. Universal and standardized procedures face many obstacles when trying to accommodate the variable and unique aspects of human minds, bodies, and environments. I have witnessed personally how the kayaking community is learning to reappreciate traditional ways of kayak construction and returning to the origins of the sport in an attempt to revive the traditions and rules of thumb that are still salvageable. In agriculture, the logic of mass production has led to immense problems with regards to soil health, biodiversity, and productivity. Here too, some old traditions are regaining appreciation. Contemporary architecture, many argue, has alienated the urban citizen from their living environment, and traditional rules of thumb may yet be revived to amend this.

The 20th century may have been a century of industrial mass production, but its prime output was a new era of monolithic cultures, homogeneous societies and economies, and a new geological epoch characterized by uncertain ecological systems and climates. When the standardized and optimized global production ecosystem19 starts to cough, human societies will inevitably meet a revived demand for diverse cognitive and cultural systems that have the requisite variety to cope with external perturbations.20 In such an uncertain environment, mass produced modes of human cognition will not suffice, and vernacular responses will be necessary. In an extraordinarily ironic turn, the standardization machine imagined by Taylor, which all but led to the extinction of local knowledge, has wreaked such havoc that the demand for local solutions is reviving. Perhaps rules of thumb will live to fight another day.


  1. Taylor, Frederick Winslow. 1919. The Principles of Scientific Management. Harper & brothers.
  2. Scott, James C. 1998. Seeing Like a State: How Certain Schemes to Improve the Human Condition Have Failed. Yale University Press.
  3. Tversky, Amos, and Daniel Kahneman. 1974. “Judgment under Uncertainty: Heuristics and Biases.” Science 185 (4157): 1124–31.
  4. Thaler, Richard H., and Cass R. Sunstein. 2008. Nudge: Improving Decisions about Health, Wealth, and Happiness. New Haven: Yale University Press.
  5. Todd, Peter M., and Gerd Gigerenzer. 2012. Ecological Rationality: Intelligence in the World. OUP USA.
  6. Haselton, Martie G., Gregory A. Bryant, Andreas Wilke, David A. Frederick, Andrew Galperin, Willem E. Frankenhuis, and Tyler Moore. 2009. “Adaptive Rationality: An Evolutionary Perspective on Cognitive Bias.” Social Cognition 27 (5): 733–63.
  7. Marewski, Julian N., Wolfgang Gaissmaier, and Gerd Gigerenzer. 2010. “Good Judgments Do Not Require Complex Cognition.” Cognitive Processing 11 (2): 103–21.
  8. Simon, Herbert A. 1990. “Invariants of Human Behavior.” Annual Review of Psychology 41 (1): 1–20.
  9. Kaaronen, Roope Oskari, Mikael A. Manninen, and Jussi T. Eronen. 2021. “Rules of Thumb and Cultural Evolution: How Simple Heuristics Have Guided Human Adaptation and the Emergence of Cultural Complexity.” PsyArXiv.
  10. Lipka, J., C. Jones, N. Gilsdorf, K. Remick, and A. Rickard. 2010. “Kayak Design: Scientific Method and Statistical Analysis (Part of the Series Math in a Cultural Context: Lessons Learned from Yup’ik Eskimo Elders).” Calgary: Detselig.
  11. Wilson, Robert A., and Lucia Foglia. 2011. “Embodied Cognition.” Stanford Encyclopedia of Philosophy.
  12. Lantz, Trevor C., and Nancy J. Turner. 2003. “Traditional Phenological Knowledge of Aboriginal Peoples in British Columbia.” Journal of Ethnobiology 23 (2): 263–86.
  13. Kaaronen, Roope O. 2018. “The Ecology of Design.” The Side View, September.
  14. John James, “Selected Bibliography on the Cathedral of Chartres.”
  15. Alexander, Christopher, S. Ishikawa, M. Silverstein, M. Jacobson M, I. Fiksdahl-King, and S. Angel, A Pattern Language: Towns, Buildings, Construction (New York: Oxford University Press, 1977): 782, 747.
  16. Kaaronen, Roope O. The Art of Mushroom Foraging: A Phenomenological Inquiry. The Side View 1, no. 1 (2019): 22-26. See also Roope O. Kaaronen, “Mycological Rationality: Heuristics, Perception and Decision-making in Mushroom Foraging.” Judgment and Decision Making 15, no. 5 (September 2020): 630–647.
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  18. Brand, C. O., A. Mesoudi, and P. E. Smaldino. 2021. “Analogy as a Catalyst for Cumulative Cultural Evolution.” Trends in Cognitive Sciences 25 (6): 450–61.
  19. Risko, Evan F., and Sam J. Gilbert. 2016. “Cognitive Offloading.” Trends in Cognitive Sciences 20 (9): 676–88.
  20. Nyström, M., J.-B. Jouffray, A. V. Norström, B. Crona, P. Søgaard Jørgensen, S. R. Carpenter, Ö Bodin, V. Galaz, and C. Folke. 2019. “Anatomy and Resilience of the Global Production Ecosystem.” Nature 575 (7781): 98–108.
  21. Kaaronen, Roope Oskari, Mikael A. Manninen, Emery Roe, Janne I. Hukkinen, and Jussi T. Eronen. 2021. “Lessons for Human Survival in a World without Ecological Templates: What Can We Learn from Small-Scale Societies?” Ecology and Society 26 (3).