What is lean? After all these years, there is still confusion. Truth is, opinions on lean differ widely. If you like heated debates, start a discussion thread on the definition of lean on LinkedIn. Many subscribe stubbornly to their own definitions and claim others “don’t get it.” In an attempt to enlighten the debate, the Journal of Operations Management (JOM) has recently published two articles that address the question.

Lenses of lean

The first article recently published by JOM is The Lenses of Lean: Visioning the Science and Practice of Efficiency by Wallace Hopp (University of Michigan) and Mark Spearman (Factory Physics Inc.). They present four “lenses” of lean:

1. The process lens: “Lean is the pursuit of waste elimination“. This is the most common definition of lean according to Hopp and Spearman, but not very useful they admit.
2. The flow lens: “Lean seeks to minimize the cost of excess inventory, capacity, or time.” This is the better definition of lean according to the authors, but not widely used in practice.
3. The network lens: “Lean is a systematic process for reducing the cost of waste.” This definition sees lean as a continuous improvement process that requires a system-wide perspective and management focus. A prime example is the classic five lean principles of Lean Thinking (Womack and Jones, 1996).
4. The organization lens: “Lean is an organizational culture that encourages continual reduction of the cost of waste.” This definition focus on behavioral aspects. The authors highlight the example of Jeff Liker’s 14 management practices in the Toyota Way (2007; 2nd edition 2020). This is the definition that offers the most potential for understanding lean deeper, according to Hopp and Spearman.

The second article contains four critical commentaries and extensions to the above lenses. It is titled Commentaries on “The Lenses of Lean” and written by Michael A. Cusumano (MIT), Matthias Holweg (Oxford), Josh Howell (LEI), Torbjørn Netland (ETH Zurich; author of this blog article), Rachna Shah (University of Minnesota), John Shook (LEI), Peter Ward (Ohio State University/LEI), and James Womack (LEI).

If I discount myself, the authors are all famous lean thinkers, researchers, and community leaders. All have engaged with lean practice and thinking for decades. The intention of this post is not to review and summarize the rich perspectives (for that, please read the articles), but to provide a quick overview of different ways to understand lean.

Lean is not efficiency

Hopp and Spearman’s “Lenses of Lean” article suggests that lean can ultimately be seen as a “theory of efficiency.” Although all commentators believe lean can increase efficiency, none agree with this view. In my own comment, I argue that lean is just as much about effectiveness as about efficiency (or more so). This is evidenced by the pervasive customer focus in lean practice and the lean literature (see, for example, the first lean principle in Lean Thinking by Womack and Jones, 1996).

Lean is first concerned with creating and delivering a product to the customer (at the right time and place, in the right quantity, and of the right quality) and second with doing so both cost and time efficiently. Besides, many efficiency-increasing measures, including digitalization and automation, are distinctly different from lean.

Lean is not TPS

Some see lean as “the Toyota Production System (TPS) employed outside Toyota.” There is some value to this perspective because it highlights TPS, but it doesn’t capture the phenomenon of lean.

A brief historical recap: In the 1980s, researchers observed that Toyota’s production system differed distinctly from “mass production” (see, Sugimori et al., 1977, Schonberger, 1982, Hall, 1983, Shingo, 1986; Monden, 1988; Ohno, 1988). Lean research was then in its introduction phase, characterized by uncoordinated and duplicated research efforts that described and explored how Toyota’s business practices differed from those of other companies. The phenomenon was given an identity and conceptualized as just-in-time (JIT) (sometimes including total quality control, as in Schonberger, 1982). Western companies began to learn its potential (see, fór example, Sepehri, 1986) and Toyota’s transplants and joint ventures were able to replicate the TPS abroad. The article “Triumph of the Lean Production System” by Krafcik (1988) was the first to introduce the term “Lean production.” By the end of the 1980s, lean was generally considered to be identical to the TPS. The publication of The Machine that Changed the World in 1990 (Womack et al.) marked lean’s entry into the growth phase. The title “lean” enabled a community of researchers, business writers, consultants, and practitioners to develop an area of thought and action. Lean began immediately to move away from TPS by incorporating ideas and practices that went beyond what was observed at Toyota.

TPS is not lean (for anyone but Toyota)

It is perfectly possible to define lean as TPS, but it is not very helpful, nor progressive. In my view, it is also riddled with problems. First, why call TPS by another name? Second, what TPS? The TPS of 1988 or the production system Toyota uses today? Of course, Toyota has developed and improved its production system—anything else would be in violation of its own principle of kaizen. Third, the TPS is tailored by, and to, Toyota. Other companies must find their own way—taking as much inspiration as they can from the mothership of lean.

The TPS is worth studying on its own, independently of the label lean. The success of Toyota cannot be denied, and it is clear that “(…) whatever Toyota have got, it isn’t a trivial task to bottle it and sell it on” (New, 2007). For good descriptions of TPS, see the extensive work of Jeff Liker and the classics by Taiichi Ohno and Yasuhiro Monden, among others.

Lean is a business phenomenon

Evidently, lean is defined in many ways. An authoritative source is the Lean Enterprise Institute, which defines lean as “creating more value for customers with fewer resources.” A quick online search returns a myriad of alternative definitions, some of which are covered by the Lenses article and the Commentaries. I accept that there are different ways to look at lean; the Indian parable “The blind men and the elephant” reminds us that we will be less wrong with more lenses. However, I have concluded with an overarching way to look at lean: Lean is a business phenomenon.

Lean, defined as a phenomenon, manifests itself in distinct “lean” cultures, strategies, rules, technologies, work practices, and behaviors that can be observed in companies. Hence, this definition allows lean to take different forms in different contexts, which is not a weakness. An important feature of this way of looking at lean is that it allows our understanding of Lean to evolve. A challenge is that it makes it difficult to provide an operationalization of lean content that applies generically. However, the ability of lean (whatever the phenomenon is) to continue to inspire people to improve their businesses in a wide range of industries and settings is ultimately a strength.

Lean is learning

Defining lean as a business phenomenon is a good start, but it’s not an end. Describing and explaining the content and process of this phenomenon must be done to give it meaning. There are many good sources for this, but readers must critically assess what lean can mean for them. The four lenses presented above or the descriptions given in the commentaries can be adopted or adapted. In my research, I often start with the definitions that make sense for the users of lean. For example, in my research of the Volvo Group, I interpreted the Volvo Production System (Volvo’s lean program) as “lean in Volvo,” and would do the same for other organizations that have carefully developed a definition of what lean means in their setting (for example, Danaher Business System, Boeing Production System, etc).

This way of looking at lean will naturally include principles like just-in-time, kaizen, and jidoka, or practices like daily huddles, 5S, andon, and poka-yoke, but only when these principles and practices are meaningful in the given context. In the following video, I provide more insights into my own (emerging) understanding of Lean as it is applied in manufacturing.

In the concluding chapter of the Shingo Research Award-winning Routledge Companion to Lean Management (Netland and Powell, 2016), we summarized 39 chapters from 72 leading lean thinkers as follows:

"We suggest that the essence of lean—as it applies to all functional areas of the enterprise and different industries and sectors—is continuous improvement, with learning at its core."

What is your comment to the Lenses of Lean article? How do you define lean?

References
Cusumano, M.A., Holweg, M., Howell, J., Netland, T., Shah, R., Shook, J., Ward, P., Womack, J. 2021. Commentaries on “The Lenses of Lean”. Journal of Operations Management, Forthcoming
Hall, R., 1983. Zero Inventories. Dow Jones-Irwin, Homewood, IL
Hayes, R.H., 1981. Why Japanese factories work. Harvard Business Review(July), 56-66
Hopp, W.J., Spearman, M.S.2020. The lenses of lean: Visioning the science and practice of efficiency. Journal of Operations Management, Forthcoming. 
Krafcik, J.F., 1988. Triumph of the lean production system. Sloan management review 30(1), 41-51
Liker, J.K., 2004. The Toyota way: 14 management principles from the world’s greatest manufacturer. McGraw-Hill, New York
Monden, Y., 1988. Toyota production system: an integrated approach to just-in-time
Netland, T.H., Powell, D.J., 2016. A lean world. In Netland and Powell (Edt). The Routledge companion to lean management. Chapter 40. Taylor & Francis, New York
New, S.J., 2007. Celebrating the enigma: the continuing puzzle of the Toyota Production System. International Journal of Production Research 45(16), 3545 - 3554
Ohno, T., 1988. Toyota Production System: beyond large-scale production. Productivity Press, New York, NY
Schonberger, R., 1982. Japanese manufacturing techniques: Nine hidden lessons in simplicity. Simon and Schuster
Sepehri, M., 1986. Just-in-time, not just in Japan. American Production and Inventory Control Society (APICS), Falls Church, VA
Shah, R., Ward, P.T., 2003. Lean manufacturing: context, practice bundles, and performance. Journal of Operations Management 21(2), 129-149
Shingo, S., 1986. Zero quality control: Source inspection and the poka-yoke system. Productivity Press, Cambridge, MS
Sugimori, Y., Kusunoki, K., Cho, F., Uchikawa, S., 1977. Toyota production system and Kanban system materialization of just-in-time and respect-for-human system. International Journal of Production Research 15(6), 553 - 564
Womack, J.P., Jones, D.T., 1996. Lean thinking: banish waste and create wealth in your corporation. Free Press, New York, NY
Womack, J.P., Jones, D.T., Roos, D., 1990. The machine that changed the world. Rawson Associates, New York, NY