Unpacking Tacit Knowledge

People often define tacit knowledge as knowledge that you can’t put into words, but this negative definition doesn’t say what tacit knowledge is—just what it isn’t. Tacit knowledge is typically not conscious or verbalizable (Horvath et al., 1998) because of the nature of associational, pattern-matching processes, but “non-verbalizable” is a negative definition and not a defining characteristic.

Worse, this definition is too broad and vague. It encompasses all kinds of things and lumps them together so people can talk to each other about tacit knowledge and not realize that they mean different things.

I want to take a more careful look at the concept of tacit knowledge. I have been fascinated by it ever since I read Ryle’s (1949) distinction between knowing that vs. knowing how, and then Polanyi’s (1958) examination of personal knowledge.

The general idea of tacit knowledge is very important. It forms the basis of expertise and it informs efforts at knowledge management (e.g., Nonaka and Takeuchi, 1995) and training. It helps us appreciate that there is a lot more to thinking and expertise and performance than can be captured in words.

It explains how an emergency department physician can walk into a room and judge that a patient “looks sick.” It explains how Mike Riley, a British naval officer, looked at a radar blob on his screen during Desert Storm in 1991 and knew that it was an Iraqi silkworm missile coming to destroy his ship, rather than an American A-6, even though the two radar profiles were identical. Riley had no idea how he made this judgment, and he concluded that he must have ESP (Klein, 1998).

Here's another example. My youngest grandchild, Harold, was celebrating his 7th birthday. Asked what he wanted, he said that he wanted me to make fudge. Hmmm. I had made fudge in the past, perhaps 20 years earlier, but never with much success. The fudge was either a fudge soup or rock hard.

Somehow Harold remembered me telling of these failures and came away with the deluded belief that I could successfully make fudge for him. But that’s what he wanted, so I agreed.

I carefully followed the recipe, dreading the step at the end that simply said I should continue stirring the cooked mixture until it lost its gloss—whatever that meant. Then I was to pour it into the pan, assuming that it hadn’t turned into a brick.

There I was, stirring away and bracing myself for yet another failure. And then something happened. I felt the fudge start to stiffen, evoking memories from 20 years earlier. “This is the moment,” I thought. I stopped stirring and poured and—amazing. It came out fine, for the first time. Some sort of muscle memory kicked in, a memory I didn’t even know I had. This fudge example illustrates embodied knowledge, which Ryle and Polanyi discussed as did Collins (2010).

Using these and other examples, I wanted to formulate a positive definition of tacit knowledge. I found that I had to distinguish different types of tacit knowledge. I went back to the iceberg diagram I have been using (Klein, 2009)—it calls out perceptual knowledge, pattern recognition, recognition of familiarity/anomaly, mental models, and mindsets.

Tacit vs Explicit Knowledge

Source: Gary Klein

Patrick Lambe (2023) has his own description of the variety of forms of tacit knowledge: embodied skills, experiential knowledge, technical knowledge, perceptual skills, social skills, and cognitive skills. Nonaka and Takeuchi (1995) offered two categories: cognitive elements (mental models. schemata, beliefs, and paradigms), and technical elements (e.g., crafts and skills).

And dialing back 30 years, Klein and Hoffman (1993) identified expertise as “seeing the invisible” and listed several features that are aspects of tacit knowledge. In addition to a number of items mentioned above, Klein and Hoffman identified using mental models to form expectancies and using these expectancies to flag missing data and events, using mental simulation to visualize antecedents and consequences, and metacognition.

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Barbara Tversky (2019) has a different perspective. Her book Mind in Motion makes several strong assertions that bear on tacit knowledge. She describes how we can engage in thinking without words, and argues that movement, actions, and spatial awareness are the real foundations of thought, including abstract thought, not words, and that gestures and facial and body expressions count as much or more than what is being said. I see the book as an unpacking of System 1 thinking and a rich depiction of different forms that tacit knowledge can take.

The suggestions described above seem to fall into five clusters. There is nothing profound about these clusters, and I imagine that others have developed taxonomies that are more compelling. The purpose of the table is to illustrate the varieties of tacit knowledge.

Five Types of Tacit Knowledge

Source: Gary Klein

The term “tacit knowledge” can cause confusion if it leads people to speculate about ways to build tacit knowledge and to represent tacit knowledge if they don’t specify the types of tacit knowledge that they are addressing. Surely the different types have different dynamics, constraints, and limitations.

The next time we hear someone refer to tacit knowledge as a unitary phenomenon, we should be on our guard because it is so easy to downplay tacit knowledge as a vague concept. By unpacking it, we make it more salient, more relevant. We help people appreciate the aspects of expertise that can easily go unnoticed.

And now for a new definition: Tacit knowledge refers to a set of beliefs and capabilities acquired through experience and expressed through pattern-matching and recognitional types of processes.