Ernst von Glasersfeld's answers
February 1999



From: "Carraher, Shannon"

I am researching the views of teaching thinking skills in the 80’s (focusing on teaching critical/analytical thinking skills) versus the 90’s (constructivism) among educators. I have noticed that constructivists rarely mention the actual method of teaching thinking. Is this because it is basically an underlying principle? Could you point me in the direction of where I could get further references concerning this area? Thank you!

S. Carraher


Dear Ms/Mr(?) Carraher,

Constructivism is intended as a theory of knowing and learning (to know). It presupposes consciousness and basic mental operations such as "reflecting" and "abstracting". I would call these mental operations "thinking" (and you might add "remembering" and "dreaming"). I have frequently maintained that putting things into words requires reflection and therefore "learning to reflect" - but I have no idea HOW reflection is performed or learned. With Piaget, I also hold that abstraction is required for the construction of experiential object concepts (e.g. ‘tree’, ‘house’, ‘star’, etc.) and reflective abstraction for the construction of concepts such as ‘number’, ‘speed’, ‘acceleration’, etc.), and that experiential situations offer occasions for making these abstractions - but HOW they are made I don’t know. Consequently I would say, you can lead the students into situations where they MAY make abstractions, but you cannot force them to do this (Kant already said this quite clearly.). The only person I know, who has successfully worked on "teaching thinking" from a constructivist point of view, is Jack Locchead (e-mail: )I would suggest that you contact him for references of papers and books.

Best wishes,

Ernst von Glasersfeld







Dear Professor Glasersfeld,

we are studying political sciences and got to know ‘radical constructivism’ in a relatively early stage of our studies. Despite having read a fairly large amount of ‘radical constructivist’ literature we are still grappling with some problems which are of great importance for us. The following questions contain some of the problems on which we would like to hear your opinion. We want to apologize beforehand because of the length of our e-mail, but since we have no access to scholars familiar with radical constructivism we address our questions to you. We embed our questions in short outline in order to enable you to detect whether we grasped the arguments correctly.

1. The fundamental problem refers to the notion of ‘science’. You accept Maturana’s notion of ‘science’ defined as the four steps constituting the process of validating an explanation (Glasersfeld 1995: 117). This is an empirical definition as opposed to Popper’s normative one, who decrees criteria for science. Maturana gained his definition by observing the natural scientist’s actions. However, he then extends these criteria, claiming that the four steps constitute the scientific method in general and you agree with him (Glasersfeld 1987: 423). This is the point where our problems crop up. ‘Social scientists’ often adopt a different understanding of science. E.g. they either assert the necessity of the inclusion of norms in the process of ‘research’; or they make certain epistemological assumptions (marxists or feminists for instance ). Accordingly, these approaches are not covered by Maturana’s definition. If we include them into our observation what scientist are actually doing we will not be able to define science in the way Maturana does it. If on the other hand, we exclude them from the community of scientific observers, we ourselves can do this only due to a certain normative criterion (which we do not want to do). Do you see any solution for this dilemma. Or is there any flaw in our outline of the problem?

2. Maturana’s four steps of validation do not have any content before they are applied to explain a certain phenomenon. Maturana says, that ‘when two scientists do not coincide in their statements or explanations, it means that they belong to different consensual communities’ (Maturana 1988: 35). Does this not give rise to the problem that the decision whether an explanation can be considered ‘scientific’ is rather due to the plausibility of the mechanism proposed to generate this phenomenon under consideration and not to the application of the four criteria of validation per se? Otherwise it could be possible to propose a mechanism containing metaphysical elements to explain a phenomenon. This also relates to the question to which extent an explanatory mechanism is allowed to contain the possibility or necessity of interpretation; i.e. how deterministic must the mechanism be? In other words: We think that the acceptance of Maturana’s formal criterion of validation is only the necessary but not the sufficient condition of classifying an explanation as scientific.

3. Maturana declines the term ‘falsification’ and claims that it presupposes the assumption of an external reality (Maturana 1988: 35; 1998: 340) . You, on the other hand, accept the possibility of falsification in the sense of a negative feedback loop. You seem to equate a successful falsification with the case if one cannot generate an observed phenomenon by a proposed mechanism. Do you have an explanation why Maturana rejects the term?

4. Do you consider mechanisms as scientific which generate an observed phenomenon only with a certain probability (‘statistical laws’)?

5. In the moment we are working on a concept of ‘democracy’ allowing an strictly empirical definition in contrast to the predominantly normative notion employed in the so-called ‘scientific’ discussion in political sciences. The mechanism we propose appears to meet Maturana’s criteria of science. Nonetheless we are not sure, whether our procedure really is a mechanism of validation in the sense of Maturana, because we cannot observe the phenomenon and propose a generative mechanism to observe it again. Rather our notion of democracy is brougth forth by the mechanism and cannot be observed without it. Do you think there is a difference between Maturana’s concept of explanation of phenomenons and our concept of defining a term empirically? (Similar problems emerge when attempting to find a definition for example of 'society’).

6. In Glasersfeld (1995: 117) you offer a reformulation of Maturana’s criterion of validation of scientific explanations. We, however, have the impression that there are important differences both between the different versions offered by Maturana and your summary. In the version proposed in Maturana (1978) the phenomenon to be explained has actually to be brought forth by the researcher. In contrast to this version, the one proposed in Maturana (1988), wants the researcher only to suggest an explanatory mechanism and not to bring forth the phenomenon in question. And he asserts that in principle even ‘psychic and spiritual phenomena’ (Maturana 1988, 38) can be explained scientifically. Besides, he substitutes the term ‘experience’ for the notion of ‘observation’. Would you agree that the version of 1978 might expose itself to the reproach of empiricism, since it restricts the phenomena which can be tackled scientifically to those which can be observed and brought forth by the researcher. It would exclude the explanation for instance of a phenomenon like the eclipse of the sun, because the phenomenon cannot be reproduced by the researcher; let alone social phenomena like ‘society’ (cf. question 5).
Furthermore, we have some problems with your usage of the term ‘prediction’ (step 3) in your own reformulation. Does it mean the researcher actually has to generate the phenomenon to be explained as in Maturana (1978); or, do you refer to the later version (1988), i.e. to the deduction of related phenomena?

7. We are often facing the problem of norms (for example in the context of decision- making). Norms can obviously not be deduced from observations. Yet, our question is: Does radical constructivism offer any explanation how we generate and modify norms, which lead our judgements and justifications?

8. Even though you demonstrate how our concept of numbers can be derived from certain patterns of perception, mathematics is not subject to empirical tests. Our question therefore is, whether you consider mathematics or logic to be sciences. To put it more broadly: Up to which degree of abstraction do you consider phenomena or concepts as empirical and therefore belonging to empirical sciences?

Glasersfeld, Ernst von 1987: Siegener Gespraeche ueber Radikalen Konstruktivismus, in: Schmidt, Siegfried J. (ed.): Der Diskurs des Radikalen Konstruktivismus, Frankfurt a.M.: Suhrkamp, 401-440.

Glasersfeld, Ernst von 1995: Radical Constructivism. A Way of Knowing and Learning, London: The Falmer Press.

Maturana 1978: Biology of Language: the Epistemology of Reality, in: Miller, G. A../Lenneberg, Elizabeth (eds.): Psychology and Biology of Language and Thought. Essays in honour of Eric H. Lenneberg, New York, N.Y.: Academic Press, 27-63.

Maturana, Humberto R. 1988: Reality: The Search for Objectivity or the Quest for a Compelling Argument, in: The Irish Journal of Psychology 9: 1, 25-82.


With all respect

Rolf Nichelmann (
Alexander Paqueé
TU Darmstadt, Institut fuer Politkwissenschaft


Dear Messrs. Paqueé and Nichelmann,

Thank you for your questions. They are many, but as you have read a good bit of constructivism, I hope that brief answers will be sufficient. If they are not, don’t hesitate to ask again.

1. Maturana mentions conditions to govern observation in his first point and in the fourth. These are "norms" scientists have agreed on. There is no reason why they should be the same in all branches of science; they concern observation and, presumably, methods of categorizing, representing, and processing observational "data". Whether YOU consider the constraints and the models built on the resulting observations to be "science", depends on how you evaluate the viability of these models. What "epistemological assumptions" a scientist makes, is his/her affair (or funeral).

2. Maturana’s four points are a description of method, not a validation of results. If you are able to repeat someone’s observations and get compatible "data", you can say, he/she "is doing science". The models he/she constructs on the basis of these "data" will have to function not only as "explanation" but also for prediction. This, I think, is where astrologers fall short. As such, the assumption that the stars influence a person’s ontogeny is no more metaphysical than gravity, but the predictions based on it are, in my view, ambiguous at best.

3. I cannot speak for Maturana. I don’t like the term "falsification" either. I prefer "viability" or "non-viability" because this requires tests in the experiential world and is always relative to the goals chosen.

4. All induction is probabilistic - and induction is all we have to establish regularities in our experience.

5. As I understand Maturana, the "hypothetical mechanism" in his point 2 is always an invented "model". Charles Peirce’s notion of "abduction" throws some light on the process of invention or "intuition". I cannot say anything about your "generative mechanism" because I don’t know what you are proposing. (re "society": I think I have answered this question earlier on the web?)

6. As I don’t always understand Maturana, I am in no position to evaluate what he says. At the moment I am not aware of his explanation of "psychic or spiritual phenomena). I disagree with what you say about eclipses. The phenomenon CAN be reproduced by researchers, because the stated conditions of observation contain temporal indications which are calculated on the basis of an accepted model. Prediction has to be understood as the indication of conditions under which the phenomenon can be constructed again.

7. I’m sure there are many kinds of "norms". In the context of "science" they cannot be deduced from first observations but from whether or not what was developed on the basis of these observations turns out to be viable or not.

8. I would say that my definition of empirical is much the same as Locke’s, Berkeley’s, and Hume’s, namely anything based on experience - and experience includes thinking as much as perceiving. I therefore would ask what is a science that is not empirical? I think I have always avoided the term "empirical sciences". The operations that generate the concept of number are MENTAL operations triggered originally by perceptual material and then made autonomous by reflection. Of course you can call mathematics a "science", but this hides the fact that mathematics does not require observation, it takes place in the abstract realm of reflection, thinking about thinking. I think this goes for classical logic, too; but Spencer Brown’s calculus of distinctions may include more.

That’s enough for today. Thank you for your interest and best wishes,

Ernst von Glasersfeld




Subject: Intersubjectivity

From: mangoo park

Dear Professor von Glasersfeld:

I am a graduate student in mathematics education. I think that I am getting to construct my knowledge of constructivism. However, I recognize that it is not easy to interpret as exactly(?) what you intended to say. Especially, I would like to ask about "shared knowledge." You explained this as "sharing a bottle of wine" in July, 1997. Could you explain in more detail how we come to share our knowledge? What's going on inside of our individual's head and among us when we come to, so called, intersubjectivity? Thank you.

p.s. I wonder that there is an error or typo in your wonderful book (Radical constructivism: A way of knowing and learning, 1995)--first line of page 181.


Dear Mr. Mangoo Park,

Thank you for your question and even more for finding an error in my book! After copy editors, proof readers, four years of distribution and about a dozen reviews, you are the first to draw attention to this silly mistake. The worst, of course, is that I must have written it. But I am very grateful to know - if there is a new edition, I might be able to correct it.

My example of the bottle of wine was to explain my view of "shared meaning", not knowledge. The meaning you attribute to a given word (or words in general) is something you have associated with the word in the course of your experience (having heard the word and having tried to use it yourself). This course of experience is necessarily different from mine or that of other speakers. You will be said to "know" the word when you use it in ways that are compatible with the way others use it. But compatibility does not mean sameness. At any time you may notice discrepancies between your use and that of others. It is not like a shared car, a thing to which you can point when neither he nor your friend is using it, hoping that his perceptual construction of it will be similar enough to yours, so that there is no argument about which car you have in mind. It makes no difference that your "image" of the car is different from his.

"Shared knowledge" is again a somewhat misleading metaphor, because your knowledge (concepts, schemes of action and of thinking) is no less your own construction than the meaning of words. However, if you infer from your observation of others, and others infer from observing you, that the way you do things and the way you approach a problem is compatible with theirs, you and they may speak of "similar" or "compatible knowledge". But, as before, this requires no more than that the situations that have been considered have not brought out discrepancies. It does not imply sameness but is sufficient to speak of "intersubjectivity" as opposed to "objectivity", which would require knowledge of things as they are independently of your or anyone’s experience.

Best wishes,

Ernst von Glasersfeld




Subject: Concepts and schemes from the perspective of constructivism

Dear Professor von Glasersfeld,

I understand that both 'concepts' and 'schemes' are mental structures that we construct or abstract from our interactions with the experiential world. My question is: How do they relate to each other and where do they differ?

Thank you.

Goh P.C.


Dear Mr. Goh,

Thank you for your interest and your question. My answer is based on MY interpretation of Piaget's ideas. "Concepts" are unitary results of abstraction, either from sensorimotor experience, or from specific actions or operations. They mostly constitute the meanings of words. What you think of when you hear "chair", "electron", "left-hand turn", "tiger", are concepts - YOUR concepts of these items, to be precise. "Schemes" are patterns of action or thinking. They consist of three parts. Assume you are entering a forest. You isolate something in your visual field that brings up the concept of "tiger" (assimilation/recognition); with this experience you have associated the instruction: "Don't run - move away slowly!" (This is the action-part of the scheme); "to save your life" is its expected result. If you experience this several times (and get away!), you may have the opportunity to "improve" (accommodation) the action of moving away; or you may learn to differentiate dangerous from friendly tigers (also an accommodation). In this sense, concepts are unitary, whereas schemes consist of three parts. By reflecting upon a particular scheme, you may conceptualize it as a unit - and then you will have constructed a concept OF the scheme. I hope this explanation will be helpful in sorting things out.

Best wishes, Ernst von Glasersfeld




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