Tacit knowledge (as opposed to formal, codified or explicit knowledge) is the kind of knowledge that is difficult to transfer to another person by means of writing it down or verbalizing it. For example, stating to someone that London is in the United Kingdom is a piece of explicit knowledge that can be written down, transmitted, and understood by a recipient. However, the ability to speak a language, use algebra, or design and use complex equipment requires all sorts of knowledge that is not always known explicitly, even by expert practitioners, and which is difficult or impossible to explicitly transfer to other users.
While tacit knowledge appears to be simple, it has far reaching consequences and is not widely understood.
The term “tacit knowing” or “tacit knowledge” was first introduced into philosophy by Michael Polanyi in 1958 in his magnum opus Personal Knowledge. He famously introduces the idea in his later work The Tacit Dimension with the assertion that “we can know more than we can tell.”. According to him, not only is the knowledge that cannot be adequately articulated by verbal means, but also all knowledge is rooted in tacit knowledge in the strong sense of that term.
With tacit knowledge, people are not often aware of the knowledge they possess or how it can be valuable to others. Effective transfer of tacit knowledge generally requires extensive personal contact, regular interaction  and trust. This kind of knowledge can only be revealed through practice in a particular context and transmitted through social networks. To some extent it is "captured" when the knowledge holder joins a network or a community of practice.
Some examples of daily activities and tacit knowledge are: riding a bike, playing the piano, driving a car, and hitting a nail with a hammer.
The formal knowledge of how to ride a bicycle is that in order to balance, if the bike falls to the left, one steers to the left. To turn right the rider first steers to the left, and then when the bike falls right, the rider steers to the right. You may know explicitly how turning of the handle bars or steering wheel change the direction of a bike or car, but you cannot simultaneously focus on this and at the same time orientate yourself in traffic.
Similarly, you may know explicitly how to hold the handle of a hammer, but you cannot simultaneously focus on the handle and hit the nail correctly with the hammer. The master pianist can perform brilliantly, but if he begins to concentrate on the movements of his fingers instead of the music, he will not be able to play as a master. Knowing the explicit knowledge, however, is no help in riding a bicycle, doesn’t help in performing well in the tasks since few people are aware of it when performing and few riders are in fact aware of this.
Tacit knowledge is not easily shared. Although it is that which is used by all people, it is not necessarily able to be easily articulated. It consists of beliefs, ideals, values, schemata and mental models which are deeply ingrained in us and which we often take for granted. While difficult to articulate, this cognitive dimension of tacit knowledge shapes the way we perceive the world.
In the field of knowledge management, the concept of tacit knowledge refers to a knowledge possessed only by an individual and difficult to communicate to others via words and symbols. Therefore, an individual can acquire tacit knowledge without language. Apprentices, for example, work with their mentors and learn craftsmanship not through language but by observation, imitation, and practice.
The key to acquiring tacit knowledge is experience. Without some form of shared experience, it is extremely difficult for people to share each other's thinking processes
Tacit knowledge has been described as “know-how” – as opposed to “know-what” (facts), “know-why” (science), or “know-who” (networking). It involves learning and skill but not in a way that can be written down. On this account knowing-how or embodied knowledge is characteristic of the expert, who acts, makes judgments, and so forth without explicitly reflecting on the principles or rules involved. The expert works without having a theory of his or her work; he or she just performs skillfully without deliberation or focused attention 
Tacit knowledge vs. Explicit knowledge: Although it is possible to distinguish conceptually between explicit and tacit knowledge, they are not separate and discrete in practice. The interaction between these two modes of knowing is vital for the creation of new knowledge.
Differences with explicit knowledge
Tacit knowledge can be distinguished from explicit knowledge in three major areas:
Codifiability and mechanism of transferring knowledge: while explicit knowledge can be codified, and easily transferred without the knowing subject, tacit knowledge is intuitive and unarticulated knowledge that cannot be communicated, understood or used without the ‘knowing subject’. Unlike the transfer of explicit knowledge, the transfer of tacit knowledge requires close interaction and the buildup of shared understanding and trust among them.
Main methods for the acquisition and accumulation: Explicit knowledge can be generated through logical deduction and acquired through practical experience in the relevant context. In contrast, tacit knowledge can only be acquired through practical experience in the relevant context.
Potential of aggregation and modes of appropriation: Explicit knowledge can be aggregated at a single location, stored in objective forms and appropriated without the participation of the knowing subject. Tacit knowledge in contrast, is personal contextual. It is distributive, and cannot easily be aggregated. The realization of its full potential requires the close involvement and cooperation of the knowing subject.
The process of transforming tacit knowledge into explicit or specifiable knowledge is known as codification, articulation, or specification. The tacit aspects of knowledge are those that cannot be codified, but can only be transmitted via training or gained through personal experience. There is a view against the distinction, where it is believed that all propositional knowledge (knowledge that) is ultimately reducible to practical knowledge (knowledge how).
Transmission models for tacit knowledge
A chief practice of technological development is the codification of tacit knowledge into explicit programmed operations so that processes previously requiring skilled employees can be automated for greater efficiency and consistency at lower cost. Such codification involves mechanically replicating the performance of persons who possess relevant tacit knowledge; in doing so, however, the ability of the skilled practitioner to innovate and adapt to unforeseen circumstances based on the tacit "feel" of the situation is often lost. The technical remedy is to attempt to substitute brute-force methods capitalizing on the computing power of a system, such as those that enable a supercomputer programmed to "play" chess against a grandmaster whose tacit knowledge of the game is broad and deep.
The conflicts demonstrated in the previous two paragraphs are reflected in Ikujiro Nonaka's model of organizational knowledge creation, in which he proposes that tacit knowledge can be converted to explicit knowledge. In that model tacit knowledge is presented variously as uncodifiable ("tacit aspects of knowledge are those that cannot be codified") and codifiable ("transforming tacit knowledge into explicit knowledge is known as codification"). This ambiguity is common in the knowledge management literature.
Nonaka's view may be contrasted with Polanyi's original view of "tacit knowing." Polanyi believed that while declarative knowledge may be needed for acquiring skills, it is unnecessary for using those skills once the novice becomes an expert. And indeed, it does seem to be the case that, as Polanyi argued, when we acquire a skill we acquire a corresponding understanding that defies articulation 
One of the most convincing examples of tacit knowledge is facial recognition. ‘‘We know a person’s face, and can recognize it among a thousand, indeed a million. Yet we usually cannot tell how we recognize a face we know, so most of this cannot be put into words.’’ When you see a face you are not conscious about your knowledge of the individual features (eye, nose, mouth), but you see and recognize the face as a whole 
Another example of tacit knowledge is the notion of language itself – it is not possible to learn a language just by being taught the rules of grammar – a native speaker picks it up at a young age almost entirely unaware of the formal grammar which they may be taught later. Other examples are how to ride a bike, how tight to make a bandage, or knowing whether a senior surgeon feels an intern may be ready to learn the intricacies of surgery; this can only be learned through personal experimentation.
Collins showed  that Western laboratories long had difficulties in successfully replicating an experiment (in this case, measuring the quality, Q, factors of sapphire) which the team led by Vladimir Braginsky at Moscow State University had been conducting for twenty years. Western scientists became suspicious of the Russian results and it was only when Russian and Western scientists conducted the measurements collaboratively that the trust was reestablished. Collins argues that laboratory visits enhance the possibility for the transfer of tacit knowledge.
Another example is the Bessemer steel process – Bessemer sold a patent for his advanced steel making process and was sued by the purchasers who couldn't get it to work. In the end Bessemer set up his own steel company because he knew how to do it, even though he could not convey it to his patent users. Bessemer's company became one of the largest in the world and changed the face of steel making.
As apprentices learn the craft of their masters through observation, imitation, and practice, so do employees of a firm learn new skills through on-the-job training. When Matsushita started developing its automatic home bread-making machine in 1985, an early problem was how to mechanize the dough-kneading process, a process that takes a master baker years of practice to perfect. To learn this tacit knowledge, a member of the software development team, Ikuko Tanaka, decided to volunteer herself as an apprentice to the head baker of the Osaka International Hotel, who was reputed to produce the area’s best bread. After a period of imitation and practice, one day she observed that the baker was not only stretching but also twisting the dough in a particular fashion (“twisting stretch”), which turned out to be the secret for making tasty bread. The Matsushita home bakery team drew together eleven members from completely different specializations and cultures: product planning, mechanical engineering, control systems, and software development. The “twisting stretch” motion was finally materialized in a prototype after a year of iterative experimentation by the engineers and team members working closely together, combining their explicit knowledge. For example, the engineers added ribs to the inside of the dough case in order to hold the dough better as it is being churned. Another team member suggested a method (later patented) to add yeast at a later stage in the process, thereby preventing the yeast from over-fermenting in high temperatures.
Knowledge management can be considered the dynamic process of creating new knowledge, identifying sources of this new knowledge and the elicitation and distribution of this knowledge. The identification of tacit knowledge sources and the creation of knowledge through tacit to tacit knowledge sharing and tacit to explicit knowledge sharing are fundamental to this process.
According to Parsaye, there are three major approaches to the capture of tacit knowledge from groups and individuals. They are:
Learning by being told.
Learning by observation.
Interviewing experts can be done in the form of structured interviewing or by recording organizational stories. Structured interviewing of experts in a particular subject is the most commonly used technique to capture pertinent, tacit knowledge. An example of a structured interview would be an exit interview. Learning by being told can be done by interviewing or by task analysis. Either way, an expert teaches the novice the processes of a task. Task analysis is the process of determining the actual task or policy by breaking it down and analyzing what needs to be done to complete the task. Learning by observation can be done by presenting the expert with a sample problem, scenario, or case study and then observing the process used to solve the problem.
All of these approaches should be recorded in order to transfer the tacit knowledge into reusable explicit knowledge.
Professor Ikujiro Nonaka has proposed the SECI (Socialization, Externalization, Combination, Internalization) model, one of the most widely cited theories in knowledge management, to present the spiraling knowledge processes of interaction between explicit knowledge and tacit knowledge (Nonaka & Takeuchi 1995).
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