What are the types of knowledge? Tacit, explicit, procedural and more
Why sources count three, four or seven types of knowledge, where each list comes from, where they agree and disagree, and what each type needs at work.
There is no single, official list of the types of knowledge. In organisations, the most common split is between explicit knowledge, which is written down or easy to write down, and tacit knowledge, which comes from experience and is hard to put into words. Psychology uses another split: declarative knowledge (knowing that something is true) and procedural knowledge (knowing how to do something). Education and philosophy each have their own lists.
This is why one page lists three types, another four and a third seven. They do not sort the same thing. This guide shows the main frameworks, who wrote each one and when, where they agree and where they contradict each other. It ends with what each type needs in practice, so that knowledge does not leave with the person who holds it.
Why sources count three, four or seven types
Each framework answers a different question:
- Can it be put into words? This gives explicit, implicit and tacit knowledge, the terms used in knowledge management.
- What is it about? Knowing that, knowing how, knowing when to use what you know: the terms used in philosophy, cognitive psychology and education.
- Who holds it? One person, a team, or the organisation itself, through its rules and routines. Institutional knowledge belongs here.
Lists of seven types or more mix these questions, and often add terms from philosophy, such as a priori and a posteriori knowledge. So one piece of knowledge often fits several types at once. Knowing how to diagnose a fault is procedural knowledge. It is partly tacit, and it is collective if the whole team shares it.
The main frameworks side by side
| Framework | Author and year | Types | What it sorts by |
|---|---|---|---|
| Tacit knowing | Michael Polanyi, 1966 | a tacit part in all knowledge | what we know but cannot tell |
| SECI model | Ikujiro Nonaka, 1994; with Hirotaka Takeuchi, 1995 | tacit, explicit | how easy it is to express, and how one becomes the other |
| Knowledge continuum | Fred Nickols, 2000 | explicit, implicit, tacit | written, could be written, cannot be written |
| Kinds of knowing | Gilbert Ryle, 1949 | acquaintance, knowing that, knowing how | what the knowledge is about |
| Memory systems | cognitive psychology (John R. Anderson, 1982; Larry Squire) | declarative, procedural | how the brain stores and uses it |
| Strategic learning | Scott Paris and colleagues, 1983 | declarative, procedural, conditional | adds when and why to use it |
| Revised Bloom's taxonomy | Lorin Anderson and David Krathwohl, 2001 | factual, conceptual, procedural, metacognitive | what a learner needs to learn |
| Organisational knowledge | Alice Lam, 2000 | embrained, embodied, encoded, embedded | tacit or explicit, individual or collective |
| Three kinds of tacit knowledge | Harry Collins, 2010 | relational, somatic, collective | why knowledge stays tacit |
Tacit and explicit knowledge
The idea of tacit knowledge comes from Michael Polanyi, a chemist who became a philosopher. In The Tacit Dimension (1966), he starts from one fact: we can know more than we can tell. His example is a face. We recognise the face of someone we know, but we cannot say how we do it. For Polanyi, tacit knowledge is not a separate category. As a 2019 review of the research quotes him, all knowledge is "either tacit or rooted in tacit knowledge".
Ikujiro Nonaka brought the idea into management. In a 1994 paper in Organization Science, he described how organisations create knowledge through a continuous dialogue between tacit and explicit knowledge. With Hirotaka Takeuchi, in 1995, he named four ways in which knowledge moves. This is the SECI model:
- socialisation, from tacit to tacit: people learn by sharing experience, like an apprentice working next to a master;
- externalisation, from tacit to explicit: people put what they know into words, models or metaphors;
- combination, from explicit to explicit: people gather and reorganise existing documents;
- internalisation, from explicit to tacit: people make a document their own by applying it.
Their best-known example, as the same review retells it, is the first fully automated home bread-making machine in Japan, launched by Matsushita in 1987. The team could not get the kneading right, because kneading was the tacit skill of master bakers. Ikuko Tanaka, a software developer, trained with a master baker. She saw that he twisted the dough as well as stretching it. She described this to the engineers as a "twisting stretch", and they designed the machine around it.
Our articles on capturing tacit knowledge and on the three types of knowledge to capture give more examples from the workplace.
Implicit knowledge: one word, two meanings
In knowledge management, implicit knowledge is knowledge that could be written down but has not been. The term comes from Fred Nickols, who wrote in 2000 that "knowledge that can be articulated but hasn't is implicit knowledge": it can be put into words, but nobody has done it yet. He placed it between explicit knowledge, which is already expressed, and tacit knowledge, which cannot be. The workaround a technician uses when a familiar tool fails is often implicit: they could explain it, but nobody has asked.
In psychology, the same word means something else. Memory researchers Larry Squire and Adam Dede describe declarative memory as "explicit" and group habits and skills under nondeclarative, or "implicit", memory (2015). In this sense, implicit knowledge is knowledge we use without being aware of it, which is close to tacit. Management research mixes the two: the 2019 review notes that some authors use "implicit knowledge" and "procedural knowledge" as other names for tacit knowledge.
So when a source says "implicit", check which meaning it uses. In the knowledge management sense, implicit knowledge is the easiest type to capture: you only need to ask the right person the right question. Our article on implicit and tacit knowledge explains the difference in more detail.
Declarative, procedural and conditional knowledge
Philosophy students learn to separate three kinds of knowledge: knowing a person or a place by acquaintance, knowing that a fact is true, and knowing how to do something, such as playing the piano. Gilbert Ryle argued in 1949 that knowing how and knowing that are distinct kinds of knowledge. Think of swimming: many people swim well and still cannot explain how they do it.
Cognitive psychology adopted the split. Declarative memory holds facts and events, which we can recall and state. Procedural memory holds skills and habits, which show in what we do rather than in what we say. In 1982 John R. Anderson described how a skill starts in a declarative stage, as facts we interpret, and moves to a procedural stage with practice. The skill then becomes faster and more automatic.
Education adds a third type. Conditional knowledge is knowing when and why to use declarative and procedural knowledge. The idea is usually traced to Scott Paris and his colleagues (1983).
Be careful with the word "procedural": it changes meaning between fields. In psychology, it mostly means skills that we cannot fully describe. In the revised Bloom's taxonomy, procedural knowledge is "how to do something" and includes methods, techniques and the criteria for using them. All of these can be written down and taught. A written procedure is procedural knowledge made explicit. Our guide on what a standard operating procedure is explains how to write one, and our article on procedural knowledge gives examples.
Institutional knowledge: a question of who holds it
Institutional knowledge is what an organisation knows about how it works: its history, its decisions, its unwritten rules, who to call. It is not a type in the frameworks above. It describes who holds the knowledge, not how it can be expressed.
In 1991, James Walsh and Gerardo Ungson asked where an organisation keeps its memory. They named five places inside it: individuals, culture, the way work is transformed into output (its procedures), structures such as roles, and the workplace itself. External archives are a sixth place, outside the organisation.
Alice Lam (2000) combines two questions: tacit or explicit, and individual or collective. This gives four forms of organisational knowledge. She and Bengt-Åke Lundvall describe them like this (2007):
| Individual | Collective | |
|---|---|---|
| Explicit | embrained: formal, theoretical knowledge learned from books and school | encoded: rules and information shared through formal systems |
| Tacit | embodied: practical skill learned through experience and apprenticeship | embedded: routines, habits and shared norms |
Harry Collins (2010) separates three kinds of tacit knowledge, and one of them is collective. Keeping your balance on a bicycle is somatic: the body knows it. Finding your way through city traffic is collective: it depends on rules and habits that belong to a society. Relational tacit knowledge could be described in principle, if someone made the effort.
ISO 9001 has required organisations to manage their organisational knowledge since 2015. The auditing guidance that the ISO 9001 Auditing Practices Group, experts from ISO's quality committee and the International Accreditation Forum (IAF), published in 2016 says this knowledge comes from the collective experience of the organisation and from the individual experience of its people. It adds that, for tacit or shared knowledge, document control is not enough.
Where the frameworks agree, and where they do not
The frameworks agree on three points:
- part of what we know can never be fully written down;
- knowing that and knowing how are different, and they are learned in different ways;
- knowledge is held by people, but also by teams and by the way work is organised.
They disagree on four questions:
- Can tacit knowledge be converted into explicit knowledge? Nonaka says yes: that is externalisation. Haridimos Tsoukas (2003) answers that tacit knowledge cannot be "captured", "translated", or "converted", only shown in what we do. The 2019 review sorts the research into three camps: conversion, interaction and practice. In the practice camp, tacit and explicit knowledge cannot be separated. Later, Nonaka and Georg von Krogh (2009) described tacit and explicit knowledge as points on a continuum, not two boxes.
- What does "implicit" mean? In knowledge management, what has not been written yet. In psychology, what we use without being aware of it.
- Is procedural knowledge tacit? Often, in psychology. Not always in education or at work, where much of it can be written.
- How many types are there? We found no standard that sets a number. A list of three, four or seven mostly tells you which question its author chose.
What each type needs at work
The useful framework is the one that tells you what to do. For a team, it is usually the first of the three questions: is the knowledge written, could it be written, or can it only be learned from someone? Take an IT support team:
| Type | In IT support | How to pass it on |
|---|---|---|
| Explicit | the procedure to reset an account | write it once, give it an owner and a review date |
| Implicit | a workaround that three technicians know | ask, write it down, have it checked |
| Tacit | sensing that an incident is about to escalate | pair work, observation, reviews after incidents |
| Collective | who to call when a supplier does not answer | a directory of experts, a record of decisions |
For tacit knowledge, the methods rely on people. The 2016 auditing guidance names mentoring and succession planning. Lam and Lundvall (2007) describe practical skill as learned through experience and apprenticeship, and a team's shared norms as supported by story-telling.
AI makes this difference concrete, because an AI assistant can only use what has been written or recorded. Erik Brynjolfsson, Danielle Li and Lindsey Raymond studied an AI assistant used by customer support staff. The less experienced staff gained the most, in speed and in quality (The Quarterly Journal of Economics, 2025). Their working paper suggests why: the assistant spread the best practices of the most able staff. We draw one conclusion from this: knowledge that exists only in someone's head stays out of reach of such an assistant.
What our customers do
At Ortis, a Belgian laboratory that makes plant-based health supplements, two needs went unmet. The first was explicit: a person needed a specific document. The second was tacit: a person needed to understand a market or a client situation and did not know who to ask. Today, its 125 employees search one platform for both the document and the person behind it, and an "experts corner" gathers competitive intelligence by topic. At SPIE ICS, staff turnover on the service desk is expected. When a technician leaves, what they documented stays on the platform.
This is what we build with Elium: a platform where every piece of written knowledge has an owner and a review date, and where you can also find the person who knows.
Common questions
There is no single list. In organisations, the main split is between explicit knowledge, which is written down or easy to write down, and tacit knowledge, which comes from experience. Psychology separates declarative knowledge (knowing that) from procedural knowledge (knowing how). Education adds conditional knowledge (knowing when and why).
In education, the revised Bloom's taxonomy (2001) lists factual, conceptual, procedural and metacognitive knowledge. In knowledge management, Fred Nickols (2000) links explicit, implicit and tacit knowledge to declarative and procedural knowledge: the first three say whether knowledge can be put into words, and the other two say what it is about.
Harry Collins (2010) separates relational tacit knowledge, which could be described if someone made the effort; somatic tacit knowledge, held in the body, like balance on a bicycle; and collective tacit knowledge, which belongs to a society, like the rules of a language.
No framework in this guide has seven types. Lists of seven combine types from several fields, for example explicit, implicit, tacit, declarative, procedural, a priori and a posteriori knowledge.
Polanyi (1966) started from the fact that we can know more than we can tell. Tacit knowledge is the part of what we know that we cannot state, like how we recognise a face. For him it is not a separate category: all knowledge is tacit or rooted in tacit knowledge.
Declarative knowledge is about facts and events, and we can state it. Procedural knowledge is about how to do things, and it shows in action. With practice, declarative knowledge about a skill often becomes procedural.
What an organisation knows about how it works: its history, decisions, unwritten rules and contacts. Some of it is written, much of it is held by people and teams. It describes who holds knowledge, not how it can be expressed.
Where to start
Think of one person whose departure would worry you. List what they know that nobody else knows, and sort each item: already written, could be written, can only be learned next to them. The first group needs an owner, the second a meeting to write it down, the third a person to work alongside them. To see how Elium helps you write down the first two and keep them up to date, book a demo.
Sources
- Michael Polanyi, The Tacit Dimension, 1966, University of Chicago Press.
- Ikujiro Nonaka, A dynamic theory of organizational knowledge creation, Organization Science, 1994.
- Ikujiro Nonaka and Georg von Krogh, Tacit knowledge and knowledge conversion, Organization Science, 2009.
- Haridimos Tsoukas, Do we really understand tacit knowledge?, in The Blackwell Handbook of Organizational Learning and Knowledge Management, 2003, reprinted in Complex Knowledge (Oxford University Press, 2005); archived copy of the 2002 conference paper.
- Evangelia Hadjimichael and Haridimos Tsoukas, Toward a better understanding of tacit knowledge in organizations, Academy of Management Annals, 2019 (accepted manuscript).
- Fred Nickols, The knowledge in knowledge management, Knowledge Management Yearbook 2000–2001.
- Stanford Encyclopedia of Philosophy, Knowledge how, 2021, and A priori justification and knowledge, revised 2020.
- Larry Squire and Adam Dede, Conscious and unconscious memory systems, Cold Spring Harbor Perspectives in Biology, 2015.
- John R. Anderson, Acquisition of cognitive skill, Psychological Review, 1982.
- Scott Paris, Marjorie Lipson and Karen Wixson, Becoming a strategic reader, Contemporary Educational Psychology, 1983; Gregory Schraw, Promoting general metacognitive awareness, Instructional Science, 1998.
- David Krathwohl, A revision of Bloom's taxonomy: an overview, Theory Into Practice, 2002.
- James Walsh and Gerardo Ungson, Organizational memory, Academy of Management Review, 1991.
- Alice Lam, Tacit knowledge, organizational learning and societal institutions, Organization Studies, 2000; Alice Lam and Bengt-Åke Lundvall, The learning organisation and national systems of competence building and innovation, 2007.
- Harry Collins, Tacit and Explicit Knowledge, 2010, University of Chicago Press.
- ISO/TC 176 and IAF, Auditing Practices Group guidance on organizational knowledge, 13 January 2016.
- Erik Brynjolfsson, Danielle Li and Lindsey Raymond, Generative AI at work, The Quarterly Journal of Economics, 2025, and NBER working paper 31161, 2023.