Tuesday, 10 January 2017

A draft chapter on the nature and transmission of knowledge for a medical textbook

Here is a draft chapter co-authored with the polymathic Peter Lanzer. A philosophical reader will spot that we make no attempt to say what knowledge is, post Gettier. Ho hum.


Medical practice aspires to be based on medical knowledge. This chapter starts by investigating why this is so, what the value of knowledge is. Explicit knowledge is factive: what is known must be true and truth is conducive to the success of medical interventions. But such knowledge has to be more than a matter of luck and hence depends on a pedigree: a justification or warrant. For explicit medical knowledge science now dominates that pedigree. But medicine also depends on practical knowledge (knowledge-how) which does not reduce to explicit knowledge (knowledge-that) whose pedigree is the development of a reliable skill. Forging a connection between practical and tacit knowledge the chapter concludes with a discussion of how it is possible to teach and learn such knowledge.


Knowledge-that: propositional knowledge of facts or of what is the case. Such knowledge is often analysed as true belief with a suitable pedigree such as justification or warrant.

Knowledge-how: knowledge required to perform actions sometimes called ‘know-how’.

Tacit knowledge: by contrast with explicit knowledge, a form of knowledge that cannot be fully put into words or codified in context-independent terms. On one view, this is because tacit knowledge is knowledge-how.

Introduction: the very idea of knowledge

In modern technologically and economically driven societies, knowledge is a critical asset. It is employed to achieve economic gains, social status, competitive advantage and professional expertise. Knowledge has become a commodity, the subject of trade and object of manipulation. The nature of knowledge itself, however, is a subject of ongoing philosophical discussion and disagreement (see e.g. 1). This chapter will review some aspects of the nature of knowledge relevant to medical professional expertise. In particular it will examine medical knowledge through the lens of its pedigree: its justification or warrant. It will compare the nature and transmission of theoretical practical medical knowledge.

Medical practitioners aim to base their interventions on a secure base of medical knowledge. Obvious though this point may seem – especially to readers of a medical textbook such as this one – it is worth reflecting on why this is. What is the value of medical, or any other, knowledge?

Answering the question of the value of knowledge is difficult. It will be approached in this section via a preliminary question: what is knowledge or what does ‘knowledge’ mean? Now there might not be a very helpful or informative answer to this question. Imagine that someone asks what stickiness is or what the word ‘sticky’ means. One might reply by offering a word that means more or less the same: such as ‘tacky’. But this does not help explain the concept of stickiness so much as swap one word for it for another. Alternatively, one might offer a more substantial explanation of the concept such as ‘a tendency of a body to adhere to another on contact’. Such an explanation may more or less equate to the concept but it is not obvious that a speaker who understands the word ‘sticky’ should be able to offer such a formal definition nor that hearing the formal definition will teach the meaning of ‘sticky’ to someone who does not understand that concept since it raises further questions such as what the word ‘adhere’ means. Despite these difficulties in defining it, there is generally no difficulty in learning, understanding and teaching how to apply the word ‘sticky’. So one should approach the question of what knowledge in general is with some caution. There may not be a very helpful definition available.

Some general features of knowledge can, however be learnt from particular examples. Suppose that a clinician knows that, because it is 5pm, her patient is due for medication. If so, she must hold, or take it to be, true that it is time for his medication. That is, she must at least believe it. (‘At least’ because we often use the word ‘believe’ when we are not sure that we do know something. “Do you know that?” “Well I believe it.”)

Second, if she really does know that her patient is due for medication, then he must really be due for medication. If she has knowledge, what she believes must be true. Knowledge is said to be factive. If someone knows that hypertension can be treated by a high grain and low fat diet then it follows that hypertension can be treated by a high grain and low fat diet. Equally if it is not true that hypertension can be treated by a high grain and low fat diet then no one can know this. This example points to a difference between knowledge and belief. Beliefs can be either true or false. Knowledge by contrast must be true. There is no species of false knowledge (by contrast with claims to knowledge which turn out not to be).

Third, if the clinician in the example has knowledge, her belief cannot merely be accidentally true. Neither a reckless guess nor an ungrounded hunch can support knowledge even if they turn out to be true. They might, too easily, not have been true. Knowledge, as Plato suggests in his dialogue Meno is tethered to truths (2). In more recent terminology, knowledge ‘tracks’ truth (3).

A claim to knowledge can be undermined even when one does one’s best. Suppose the clinician believes that it is time for her patient’s medication because she knows that he takes medication every day at 5pm and she believes, by looking at the ward clock, that it is now 5pm. But suppose that the normally reliable ward clock has, in fact, stopped the day before. By lucky chance, however, it is now 5pm. If so, although the clinician has a true belief that it is time for her patient’s medication she does not know it. Her belief is merely true by luck. If she had looked at the clock an hour earlier she would have formed the false belief that it was 5pm and so time for his medication. Being lucky will make no difference to how things seem to her, since she does not realise the clock has stopped, but an observer might say that she didn’t know the time, she was right only by luck. Her claim does not track the truth about time.

To address this incompatibility between knowledge and merely lucky true belief, philosophers have long attempted to analyze knowledge as 1) a belief which is 2) true and 3) some extra ingredient which rules out luck. One longstanding definition which can be found in Plato’s dialogue the Theaetetus construes the third component as justification (4). In the more traditional order, knowledge is justified true belief. The idea is that needing a justification for a belief (for it to count as knowledge) should rule out merely lucky true beliefs. But this prompts a question: in the example of the stopped ward clock, does that work?

Consider this question for a moment. Does the traditional analysis that knowledge is justified true belief give the correct account of the case of the stopped clock? That is, does it fit our intuitions that the clinician does not know that it is time for her patient’s medication even though her belief that it is is true? Here is a clue: ask whether the clinician has a justification for thinking the time is 5pm and also ask whether her true belief is, despite that, lucky. If the answer to both is ‘yes’ then the traditional account does not address the problem of luck. If it does not, could some modification be made to the definition? We will return to this question shortly.

As well as trying to rule out merely lucky true beliefs, justification also plays a second role which is helpful for thinking about the challenge of generating medical knowledge. It provides a way, or a method, or a route, to aim at true beliefs. It is one thing to worry that one’s beliefs about the latest medication for coronary illness may not be right, but quite another to work out how to avoid being wrong.

Suppose a hospital authority issued an instruction that medical staff should replace any false beliefs they hold with true beliefs. On the face of it, this seems a good aim. But would the instruction help? Could one act on it? The problem is that ‘from the inside’ true beliefs and false beliefs seem the same. To hold a belief is to hold it to be true. To believe that something is not true is precisely not to believe it. Thus beliefs which are, in fact, false are not transparently so to someone who holds them. So the instruction is not helpful.

By contrast, the following instruction would help: medical staff should replace any beliefs that they hold without a justification with beliefs that do have justifications or grounds. In essence, this is the advice of Evidence Based Medicine (5). One can tell whether one believes something for a reason, or with a justification. And further, by aiming at having only justified beliefs, one should in general succeed in reaching true beliefs since justification is, in general, conducive to truth. Any ‘justification’ which did not increase the chances of a belief being true would not be a justification for it after all.

Although justification can play this second, helpful role of providing a concrete way of aiming at true beliefs it is not so successful in the first role mentioned above: ruling out being merely true by luck. As the example of the stopped clock illustrates, the clinician does have a justification for believing that it is 5pm: she can point to the clock. Nevertheless, her belief is only true by luck because, as the narrator of the film Withnail and I (6) says: even a stopped clock is right twice a day. So she has a justification for a belief and the belief is true but no one would say that she knows the time.

Although the definition that knowledge is justified true belief dominated philosophy for 2,000 years since Plato, the problem that one might have a justified, true belief but still not have knowledge was first pointed out in the 1960s by the philosopher Edmund Gettier using an example like this one (7). What follows?

It seems at first that, as a definition of knowledge, ‘justified, true belief’ must fail (because the clinician has justified, true belief but she does not have knowledge, she is merely lucky). But a better response is to argue that what the example really shows is that the clinician does not really have a proper justification, a good enough justification for knowledge. Knowledge can still be correctly understood as justified, true belief but not everything that one might think of as a justification (in the example, looking at the ward clock) really is a justification (because the clock has stopped). If so, it is a little like the definition of stickiness from earlier: ‘a tendency of a body to adhere to another on contact’. Just as only someone who understands the concept of stickiness will understanding the concept of adhering, so only someone who can understand the concept of knowledge can understand the kind of justification it needs. Knowledge and justification are a pair of concepts that one learns, in learning a first language, at the same time. The definition, whilst not explaining knowledge to someone who does not already understand it, highlights the essential connection between knowledge truth and its grounds: its justification or warrant.

If so, medical knowledge has to have the right kind of justification or grounding. The route to knowledge to underpin medical practice will be, as suggested above, through suitable justification.

To return to the question first raised why should medical practitioners aim to have knowledge of their subject? What is the value of knowledge? In the light of the discussion so far part of the answer is this. Because knowledge, unlike say mere rumour or public opinion on which medicine might otherwise be based, is by definition true, aiming at knowledge is aiming at truth. Now it may seem obvious in a theoretical or contemplative discipline why one should aim at truth in one’s thinking. Cosmologists, for example, want to understand how the universe works just for the sake of understanding it. And hence they should aim at knowledge and hence true beliefs just for their sake.

But there is a further reason for medical practitioners to aim at truth. This is because medicine is a practical discipline. It aims not just to understand health and illness (as a merely theoretical or contemplative discipline) but, for example, to make a difference, to change people’s states of illness to health. And in general, actions – for example, medical interventions, or acts of caring – based on true beliefs are more likely to succeed than those based on false ones. So medical practitioners should aim at having true beliefs in order that their practical interventions in the lives of their patients are more likely to be successful. But because there are no intrinsic signs or symptoms of true beliefs that mark them out from false beliefs, the route to this is via a suitable justification which forms part of the conceptually rich idea of knowledge.

However, being subject to the rapid evolution of our understanding of natural laws and nature’s first principles the shelf-life of what, at any particular time, we take to be knowledge in science and medicine is limited as illustrated by many examples where deeply held views about the functioning of the body have later been shown to be false. Because of the prominence of both exponents, the following example will suffice. As reported by Philipp Melanchton, Professor of Greek and versatile theologian at the University Wittenberg and Luther’s close friend, Luther had suffered a severe attack of angina pain on 18 February, 1546. In, Melanchton’s words (1): ‘Doctor Martin Luther called me (to see him) a year before his death at 2 in the morning. Coincidentally I was already up at the time. I went to see him and asked, what has happened. O, he said, I am experiencing great and dangerous pains. I asked him, if it was a stone. He replied: No, it is more than a stone. I felt his pulse, it was normal. I said: heart is all right, it is not a heart attack. Then he said: I have a severe tightness in my chest, yet I do not feel any heart constriction, and I do not feel any difficulties with the pulse. I pondered; it cannot be other than liquid rising up in the stomach entrance. That is the reason for the severe tightness, and the disease termed stabbing in the chest. . . . he went to a toilet; it was very cold. Immediately he felt, how he was seized by the cold and promptly by that same disease.’ (8). Despite Melanchton’s exceptional erudition, his medical knowledge based on a 16th century understanding of the body sounds absurd by present standards. At the time it no doubt seemed to be justified and hence likely to be cutting edge knowledge. Given the rapid and accelerating advancements of knowledge in life sciences and medicine, keeping up to date with the progress of knowledge and the correction of previous errors represents an increasing challenge to medical practitioners.

This section has considered a fundamental question: why should medical practitioners aim to have knowledge. ‘Unpacking’ the concept of knowledge suggests answers which connect to the value of truth, the role of justification as a way of aiming at truth and the practical ambitions of medicine to intervene in patients’ lives. There are further, complementary reasons that could have been explored. For example, to identify someone, such as a particular member of a multiple disciplinary team, as knowing a patient’s history is to mark out what he or she says on the matter as reliable. Knowledge can be used to mark out whom to trust in cooperative disciplines like medicine (9). But the idea that knowledge has to possess some suitable justification, warrant or pedigree suggests a lens through which to consider medical knowledge. Is there any general account of the warrant for medical knowledge? The next section outlines a thumbnail sketch of one element of that pedigree: the scientific basis of theoretical medical knowledge.

A short history of theoretical knowledge

Systematic or theoretical knowledge has a long history. Ancient cultures such as the Sumerians in Mesopotamia, the Shang dynasty in China, ancient Indus river cultures in India and those of Egyptian’s empires, and others – all of them considerably older than the era of Socrates – had acquired some systematic knowledge (10). The ancient Greeks, especially Aristotle, wrote widely on natural phenomena based on careful observation. Subsequently, there was an intermingling of the ideas of Plato and Aristotle with Christian doctrines. Thus for example, ‘neo-Platonism’ is the name for original ideas from Plato as interpreted by Plotinus (204-270 AD) and then mingled with Christian theology such that neo-Platonist views came to be thought of official Christian teaching.

Given the importance of something like a justification condition for knowledge, one important aspect of the history of knowledge claims about the natural world is the relation of justification by text versus empirical justification. Thus, ironically, whilst the physician Galen (129-199AD) wrote extensively about empirical demonstration for knowledge claims, his medical works themselves took on an unquestioned textual authority for several hundred years afterwards.

In fact, this distinction in approaches to justification can also be seen within the Christian theology of the medieval period between revealed theology, based on scripture, and natural theology, based on reason and experience. The latter, albeit with the intention of discovering more about the nature of God through God’s creation, served as a stimulus for the kind of empirical inquiry later found in science. Medieval scholars such as Roger Bacon stressed empirical justification rather than appealing to the revelation of God’s ultimate authority albeit as a way of discovering more about God’s creation. This also complicates the story, crystalized in Galileo’s encounter with the Inquisition, that empirical methods and Christian theology were incompatible.

On a standard account of the history of science, ‘modern science’ emerged or evolved from proto-scientific inquiry in a revolution on the seventeenth century when there was a rise in the sophistication of observation using newly developed equipment (for example, telescopes and microscopes), a development of experimentation and manipulation of natural phenomena in order to better to understand them (such as the development of the air pump) and in the development of mathematical representation of nature in codifying laws of nature (11, 12). These developments are associated with Nicolas Copernicus, Johannes Kepler, Galileo Galilee, Anton van Leeuwenhoek, William Harvey and many others. The foremost was Isaac Newton, whose opening sentence of Optics ‘My design in this book is not to explain properties of Light by Hypothesis, but to propose and prove them by Reason and Experiment: In order to which I shall premise the following definitions and axioms.’ (13) serves as the testimony to the transition from metaphysical believes to down-to-earth exact science.

More recent historiography has questioned this account. For one thing, although Newton, for example, is widely embraced as one of the founders of modern physics, he himself conceived of his work as lying within a natural theological tradition as an attempt to understand God through nature (14). For another, drawing boundaries on the ‘revolution’ has proved increasing difficult, expanding it from one century to five in order to include all the relevant founding figures (15). It has thus been plausibly argued by Andrew Cummingham and Perry Williams that the origins of ‘modern science’ would be better situated rather later in what the historian Eric Hobsbawm called the ‘Age of Revolutions’ (1760—184) marked out by the French Revolution, the Industrial Revolution in the UK and the post-Kantian intellectual revolution, centred on the German states (16, 17). That is the period, they argue, when scientists first embraced the label ‘science’ as a distinctive form of empirical inquiry into the natural world based on laboratories and also separated it from natural theological purposes. Further, they argue that such a modification of the traditional picture should go hand in hand with a rejection of the idea that science is an inevitable teleological endpoint of human development, anticipated by earlier proto-scientific forms. Hence theirs is an account of the ‘modern origins of science’ rather than the ‘origins of modern science’. Science, on their view, is a comparatively recent invention, a local and historically contingent way of finding out about the natural world for secular purposes.

Such a view chimes with the trajectory of twentieth century philosophy of science. By contrast with the optimism of the Vienna Circle in the 1930s that it would be possible to codify ‘the scientific method’, philosophers of science such as Karl Popper, Imre Lakataos and Larry Laudan have struggled to balance clear prescriptions for how scientists ought to proceed with a realistic account of methods actually followed (18-21).

Consider, for example, Popper’s famous idea that scientific theories should be falsifiable and aim at refutation rather than confirmation on the grounds that a single observation can refute a general theory whilst no finite number of observations can confirm it. Such a prescription is complicated by the fact that any observation might itself be mistaken. Observations can only be made in the context of a number of other theories (for example, concerning the operation of equipment used to make them) and hence in the face of a recalcitrant observation, there is always an element of choice concerning which theory has been undermined (18). Increasingly, the task of shedding light on the methods of scientists has fallen to other scientist: social scientists specializing in scientific practice (e.g . 22, 23, 24 ). But even if there is no single scientific method which can be set out from first principles but rather a number of related methods which have evolved especially over the last two hundred years, science has increasingly provided the only pedigree and justification for knowledge of nature.

Within medicine, this has been specifically emphasized in the rise of Evidence Based Medicine, whose hierarchy of evidence stresses the role of randomized control trials (RCTs) or the meta-analysis of several RCTs over descriptive studies and the authority of respected figures (5). Medical practitioners are encouraged actively to review evolving empirical evidence for available treatment and management options, echoing the change from justification via historic textual authority to empirical evidence in both natural theology and natural science.

Besides the rapid expansion of knowledge in basic and life sciences over the last 200 years, more recently the retrieval, transfer and distribution of knowledge has been revolutionized through the progress in information and communication technology, ICT. Knowledge has become one of the most formative and critical forces with global impact (e.g. financial markets) (25).

The rise of ICT and the mass distribution of information raise a question about the lens with which this chapter has looked at knowledge: its justification or warrant. The challenge is this: if the end user of a piece of information is separated by many steps from its original production how can he or she ensure that it is justified? If knowledge is more than true belief, how can it be shared electronically across the globe?

One answer to this question is motivated in part by Gettier’s challenge to the idea that knowledge is justified true belief. It may seem natural to think that the person who knows something must also know its justification. But that may not be so. If the purpose of the third condition on knowledge is to counter the knowledge-undermining effects of luck this may not be a matter for each individual as long as general systems of knowledge production and transfer actually are reliable (whether or not anyone knows this additional fact). The rise of modern science has helped to promote the idea that knowledge can be a collective, as well as an individual, enterprise.

Theoretical and practical knowledge

The previous section offered a thumbnail sketch of the development of theoretical knowledge and the invention of science as a secular, laboratory-based empirical study of nature for its own sake. Theoretical knowledge is, however, merely one of the forms of knowledge on which modern medicine is based. The ancient Greeks distinguished between theoretical and practical forms of knowledge. The Greek word epistêmê is usually translated as theoretical knowledge or, we might now say, scientific knowledge. It contrasts with technê which means something like craft or art. In fact, Aristotle suggested that there were five ‘virtues’ associated with knowledge adding to epistêmê and technê, phronêsis, sophia, and nous which are variously translated but the first of which, phronêsis, is also relevant here. Phronêsis is practical wisdom: practical in a sense, like technê, of concerning how to change aspects of the world but also practical in the sense (distinct from technê) of concerning how one ought to act. (For further readings see e.g. 26).

In the twentieth century, Gilbert Ryle emphasised the importance of a distinction which resembles the distinction between, on the one hand, epistêmê and, on the other, technê and phronêsis (27) Ryle 1949). Ryle’s distinction is between knowing-that and knowing-how. Further, he stressed the priority of practical of procedural knowing-how over declarative knowledge-that. Against what he called an ‘intellectualist legend’, he rejected the view that intelligent practical knowledge has to be based on underlying knowledge-that in the form of grasping a principle or proposition. Ryle argued, instead, that ‘[i]ntelligent practice is not a step-child of theory’ (Ryle 1949:27 italics added). In fact, in stressing the priority of practical knowledge over theoretical knowledge, Ryle echoed the views of two other influential twentieth century philosophers: Martin Heidegger and Ludwig Wittgenstein both of whom stressed the practical grounding of intellectual knowledge (28, 29).

At about the same time, a different distinction between kinds of knowledge was promoted by the chemist turned philosopher of science, Michael Polanyi. He contrasted tacit with explicit knowledge (Polanyi 1958). Polanyi starts his book The Tacit Dimension with the following slogan: ‘I shall reconsider human knowledge by starting from the fact that we can know more than we can tell’ (30) Polanyi 1967: 4) But as he immediately concedes, the slogan is gnomic. Does it carry, for example, a sotto voce qualification ‘at any one particular time’? Or does it mean: ever? He continues:

This fact seems obvious enough; but it is not easy to say exactly what it means. Take an example. We know a person’s face, and can recognize it among a thousand, indeed among a million. Yet we usually cannot tell how we recognize a face we know. So most of this knowledge cannot be put into words. [Polanyi 1967b: 4]

Polanyi’s work has prompted the study of tacit knowledge across a range of contexts including business organizations and professions (for further reading see the specialized literature eg (31) e.g. Sternberg and Horvath 1999). But the nature of tacit knowledge has been contested (32, 33).

Bringing Ryle’s and Polanyi’s concepts together suggests the following idea: knowledge-that is explicit knowledge and being explicit is therefore codifiable, accessible, promptly transferred via ICT. But it has no direct connection to action. By contrast, tacit knowledge understood as knowledge-how is critical to the performance of actions but is not codifiable in context-independent terms and hence is transmitted remotely, for example via ICT, only with difficulty.

Applying this distinction to medical knowledge, the tradition has it that physicians are masters of knowledge-that while surgeons are masters of knowledge-how. Appealing though this simple classification may appear, it is clearly wrong as a distinction of kind. While it is true that the professional competence of non-surgeons emphasizes knowledge-that and that of surgeons knowledge-how, the main difference between the two professional groups consists in the relative mix or the degree of required theoretical and practical knowledge or cognitive and psycho-motor skills. Taking into account the upsurge of new surgical techniques (e.g. minimally invasive, often catheter-based techniques) performed by both surgeons and non-surgeons such a simple distinction between the two groups fails. Clearly, in the new formats of medical disciplines, the right mix of specific knowledge-that and knowledge-how determines the relevant expertise.

Is practical knowledge a genuine form of knowledge?

The first section of this chapter illustrated the immiscibility of knowledge and luck and hence the need for knowledge to possess a suitable pedigree, warrant or justification. That need was illustrated for the case of knowledge-that, or explicit, or theoretical knowledge (using the example that it was time for a patient’s medication). If that is a general requirement for knowledge, does practical knowledge (or tacit knowledge or know-how) count as a proper species of knowledge?

If practical knowledge (or know-how) could be analysed as a form of theoretical knowledge (or knowledge-that) then the former could inherit the same sort of warrant or justification as the latter. So if practical knowledge of how to do something could always be encoded in grasp of the truth of some principle of how to do it, it would clearly count as a sub-species of genuine knowledge. So does knowledge-how depend on prior knowledge-that? The assumption that it does is what Ryle calls the ‘intellectualist legend’, mentioned above. His argument against it is that if knowing how depends on grasping a piece of explicit knowledge, such as grasping a principle which encodes how to do something, then such grasping is itself a skill which can be exercised well or badly. And so, according to the intellectualist legend, there will need to be another piece of explicit knowledge which underpins how the first piece is grasped. But that leads to a vicious infinite regress. (For an opposing view see 34).

Instead, Ryle argues, knowledge-how is more basic than knowledge-that and stands in no need explanation in terms of knowledge-that. Skills are fundamental. (It is a further question, on which we will not touch here, whether knowledge-that can be analysed as knowledge-how. But a lesson of the twentieth century seems to be that explicit knowledge-that does depend on practical knowledge-how.)

If knowledge-how is not underpinned by knowledge-that, what is the status of its justification? The connection between knowledge-how and skill, emphasised by both Ryle and Polanyi, suggests the answer. The novice’s first time luck in sinking a golf ball is not a piece of knowledge-how because it is a matter of beginner’s luck. Skilful performance, by contrast, is successful because it is based on a longstanding capacity honed through practice and criticism. So the equivalent of the justification of knowledge-that is developing a genuine skill for knowing how to do something: an enduring capacity or reliable ability.

Skills can be performed with a wide range of expertise: from the first steps of novices up to the highest levels of virtuosity of masters. Dreyfus and Dreyfus developed a five stage model of the acquisition of skills in which a novice starts by grasping context-independent rules and following them but in time and through practice proceeds in the direction of true practical expertise which transcends rules and guidelines and depends instead of flexible recognition of the demands of particular situations (35). This model has been influential in medical education (e.g.36). But although it starts with the following of rules it is in accord with Ryle’s view that expert know-how does not depend on knowledge-that but is free-standing. The Dreyfus and Dreyfus model provides one element in answer to the question raised in the final section of this chapter. How can practical knowledge be taught and acquired?

The explication and transfer of practical knowledge

Perhaps on the basis of Polanyi’s label ‘tacit’, it has often been assumed that while explicit knowledge is communicable, tacit knowledge is not. This intuitive, but questionable, connection between its tacit status and the difficulty of assessing it is a key feature of an empirical study of the know-how required to build a working laser by the contemporary sociologist of science Harry Collins. Finding that published accounts (ie. explicit knowledge) of a newly developed laser were insufficient to enable others to build a working laser, he discovered that the communication of knowledge of how to build a laser required a personal connection and was ‘capricious’.

In sum, the flow of knowledge was such that, first, it travelled only where there was personal contact with an accomplished practitioner; second, its passage was invisible so that scientists did not know whether they had the relevant expertise to build a laser until they tried it; and, third, it was so capricious that similar relationships between teacher and learner might or might not result in the transfer of knowledge. These characteristics of the flow of knowledge make sense if a crucial component in laser building ability is ‘tacit knowledge’. (37).

The view that practical knowledge is necessarily invisible and capricious is, however, questionable. Whether or not it is part of Polanyi’s contrast, it is not part of Ryle’s account of the distinction between knowing how and knowing that. The elicitation, codifiability, transformations and transfer of knowledge-that and knowledge-how are, however, works-in-progress in both, basic and applied cognitive sciences. In fact, they constitute the very core of a now hot research field of cognitive teaching and learning (38-40).

In the medical professional context, strategies and techniques have been developed and are now available to explicate and to teach some, if certainly not all of forms of expert knowledge-how. The former belief that procedural expertise in a professional context results merely from long repetitive practice plus some special gifts or talents is no longer tenable.

Thanks to the work of Ericsson and associates, the principle of deliberate practice as the foundation of virtually any professional expertise has been established (41). Deliberate practice focuses on supervised, conscious, dedicated and repetitive enacting of specific parts of the whole task allowing first grasping and then fine-tuning of their performance. To be successful, deliberate practice requires comprehensible instruction, a sufficient number of repetitions and expert feed-back for corrections. Thus, in the vast majority of cases, true professional expertise, along with the discovery of novel knowledge in some cases, are achieved, paid for by long years of deliberate practice with strokes of genius being limited to important but rare instances.

For such training and education to be effective, however, expert knowledge must first be elicited. Developed by cognitive psychologists, different strategies such as observations, verbal reports and interviews have been employed to elicit and to represent expert knowledge summarily denoted as ‘cognitive task analysis’ (CTA) (42). Subsequently, more elaborate and didactically updated teaching programs have been designed (43) see van Merrienboer and Kirschner 2007).

The transfer of expert knowledge is the essence of all teaching and learning. Over the years much has been published on the similarities and differences between explicit and implicit learning along with lists of theories and models extant in the literature (see e.g. 44, 45). For the purposes of this chapter, a simplified brief presentation of the techniques of knowledge transfer applicable to practice of medical education will suffice.

Traditionally, the transfer of medical and invariably explicit knowledge-that was based on lectures and textbooks. Students learnt via verbal instruction and reading texts. With recent advances in information and communication technology, ICT, new forms of visual and auditory learning assistance have been developed. However, despite these advances, the effective absorption of such explicit medical knowledge-that still requires, above all, data crunching and cramming.

By contrast with the focus on the transfer of explicit knowledge-that in a medical education, the transfer of the mostly implicit knowledge-how has been largely ignored. With the rare exception of some excellent texts on surgery and surgical techniques, in the majority of textbooks knowledge-how has been either taken for granted and avoided or its surface has been, merely, scratched often by providing some ‘tips and tricks’ and time-proven recipes.

In practical education, knowledge-how has been mostly taught within the framework of the traditional ‘mentor-trainee’ relationship. Using this approach typically knowledge-how has been represented as readymade cognitive and/or psycho-motor skills. These skills are demonstrated by the mentor and subsequently imitated and emulated by the trainee. The efficiency of this approach is highly dependent on the ability and skills of the mentor, to demonstrate, and those of the trainee, to imitate, embody and emulate. It has been only recently that a cognitive approach to the transfer of knowledge-how, already proven to be effective in number of other professions, has been adopted in some medical institutions to train physicians to perform specific surgical and anesthesia-related procedures.

To employ this approach successfully, expert knowledge-how has to be articulated and explicated (in simple, well standardized procedures, this may be a relatively straightforward task), verbalized as far as possible and employed to instruct the trainee to perform specific actions. These actions are then practiced with deliberation by the trainee, mostly in model or paradigmatic contexts, observed and corrected, if necessary, by the mentor. Straightforward tasks may be explicated and dissected in a linear series of premeditated steps; more advanced tasks can be divided into (repetitive) patterns for simplification. Highly complex tasks are based on the internalization of whole networks of skills and may therefore be difficult to characterize. Partial explication, only, may be possible. The teaching of complex cognitive tasks in medicine has not yet been systematically approached. Recently, in the context of percutaneous coronary interventions, PCI, Lanzer and Taatgen have proposed developing and exploiting generic strategies and tactics allowing trainees to understand the procedural logic behind decisions in order to develop and hone their own judgment and decision making skills (46). Residual, as yet uncodifiable knowledge, remains proprietary to individual highly skilled operators. These skills have occasionally been termed ‘intuition’.

The transfer of knowledge-how is an active process requiring understanding of the tasks which are proposed and practiced (47). Thus, the knowledge-how must be embodied, i.e. internalized through (deliberate) practice. Therefore the success of knowledge-how transfer is highly dependent on active, focused and vigilant participation of trainees in the learning process and their ability to internalize complex cognitive structures and processes. A number of cognitive techniques have been proposed to enhance and facilitate such transfer. Recently, for example, contextual teaching - by providing contextual and associative information - has been shown to improve the retention and understanding of knowledge-how (48).

While knowledge-how can sometimes be acquired on-the-job, especially in high-risk tasks, a supervised ‘off-line’ teaching environment is (at least initially) required. Subsequent ‘on-line-real-time’ teaching is then often the final step of the process. Furthermore, tasks requiring complex cognitive skills such as the implementation of case-related strategies and tactics and/or those demanding finely tuned hands-eyes coordination are always best learned “off-line”.

Within the medical profession, the transfer of knowledge-that and knowledge-how should be better regulated, supervised and quality controlled. While for example in aviation, all the steps of the process have been tightly regulated (by the Federal Aviation Administration), in medicine, by comparison, it is mainly only the processes associated with acquisition of knowledge-that have been quality controlled, and even there no international standards exist. Sadly, the acquisition of medical knowledge-how still relies in most cases on the time-tested yet in principle still medieval ‘mentor-to-trainee’ practices. (To review proposals to develop knowledge- and skill- based curriculum in percutaneous coronary interventions as an example for quality controlled training in high-risk medical activity see (49).

A final note: this chapter has compared and contrasted the pedigree and transmission of theoretical and practical, or explicit and tacit, knowledge. That binary opposition may, however, be insufficient to capture the subtleties of the requirements for medical knowledge as a whole. For example, skilled clinicians must have an understanding of the states of mind of their patients. They must also be able to understand the values that should govern medical interventions: those of their patients, their own and those of the broader society. It may be that knowledge in such cases can always be mapped onto the distinction between explicit and tacit, theoretical and practical. But that should not mislead one into thinking that the nature of the justification or warrant for a claim to know the values of a particular patient, for example, will be the same – of the same kind – as the justification for knowing the population wide efficacy of a kind of surgical intervention.


Medical practice aspires to be based on medical knowledge. This chapter started by investigating why this is so, what the value is of knowledge. Explicit knowledge is factive: what is known must be true and truth is conducive to the success of medical interventions. But such knowledge has to be more than a matter of luck and hence depends on a pedigree: a justification or warrant. For explicit medical knowledge science now dominates that pedigree. But medicine also depends on practical knowledge (knowledge-how) which does not reduce to explicit knowledge (knowledge-that) whose pedigree is the development of a reliable skill. Forging a connection between practical and tacit knowledge the chapter concluded with a discussion of how it is possible to teach and learn such knowledge.


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