Journal of Consciousness Studies, 6, No. 2/3, 1999, pp. 299–306
Special double issue on The View from Within: First-person approaches
edited by Francisco J. Varela and Jonathan Shear


Max Velmans, Department of Psychology, Goldsmiths, University of London, New Cross, London SE14 6NW, UK.  Email:

Abstract: The study of consciousness in modern science is hampered by deeply ingrained, dualist presuppositions about the nature of consciousness.  In particular, conscious experiences are thought to be private and subjective, contrasting with physical phenomena which are public and objective. In the present article, I argue that all observed phenomena are, in a sense, private to a given observer, although there are some events to which there is public access. Phenomena can be objective in the sense of intersubjective, investigators can be objective in the sense of truthful or dispassionate, and procedures can be objective in being well-specified, but observed phenomena cannot be objective in the sense of being observer-free.  Phenomena are only repeatable in the sense that they are judged by a community of observers to be tokens of the same type.  Stripped of its dualist trappings the empirical method becomes if you carry out these procedures you will observe or experience these results — which applies as much to a science of consciousness as it does to physics.

From the time that Descartes separated the conscious mind (res cogitans) from the material world (res extensa) consciousness has been thought by many to be beyond science. The problems which need to be addressed by a ‘science of consciousness’ are of three kinds:

1. Epistemological problems: How can one obtain public, objective knowledge about private, subjective experiences?

2. Methodological problems: Given that one cannot attach measuring instruments directly up to experiences, what methods are appropriate to their study?

3. The relation of the observer to the observed:  The more closely-coupled an observer is with an observed, the greater the potential influence of the act of observation on the nature of the observed (observer effects).  Given this, how can one develop introspective and phenomenological methods where the observer is the observed?

Many established methods for investigating conscious experiences within cognitive science and neuropsychology are reviewed in Velmans (1996a) and Cohen & Schooler (1997). This issue of the Journal of Consciousness Studies focuses on the development of new phenomenological methods which attempt to grapple with observer/observed interactions.  An extensive treatment of methodological issues is also forthcoming in Velmans (2000a). Given the limits of available space in this article, I will restrict myself to the epistemological problems. Broadly, I will argue that the epistemological problems posed by a ‘science of consciousness’ are largely artefactual, arising from a misconceived dualism that we have inherited from Descartes.  This is clearly shown in the model of perception shown in Figure 1.  This ‘splits’ the world in two ways: (1) the observer (on the right of the diagram) is clearly separated from the observed (the light on the left of the diagram) and (2) public, objective ‘physical phenomena’ in the external world or in the brain (in the lower part of the diagram) are clearly separated from private, subjective psychological phenomena ‘in the mind’ (represented by the cloud in the upper part of the diagram).


How we make sense of this in conventional studies of perception

Following usual procedures, a subject (S) is asked to focus on the light and report on or respond to what she experiences, while the experimenter (E) controls the stimulus and tries to observe what is going on in the subject’s brain.  E has observational access to the stimulus and to S’s brain states, but has no access to what S experiences.  In principle, other experimenters can also observe the stimulus and S’s brain states.  Consequently, what E has access to is thought of as ‘public’ and ‘objective.’  However, E does not have access to S’s experiences, making them ‘private’ and ‘sub- jective’ and a problem for science.  This apparently radical difference in the epistemic status of the data accessible to E and S is enshrined in the words commonly used to describe what they perceive.  That is, E makes observations, whereas S merely has subjective experiences.

Although this way of looking at things is adequate as a working model for many studies, it actually misdescribes the phenomenology of consciousness, and consequently misconstrues the problems posed by a science of consciousness.  An alternative model of the way events in the world are experienced by subjects is shown in the reflexive model of perception in Figure 2.




This reflexive model accepts conventional wisdom about the physical and neurophysiological causes of perception — for example, that there really is a physical stimulus in the room that our experience of it represents. But it gives a different account of the nature of the resulting experience. According to this nondualist view, when S attends to the light in a room she does not have an experience of a light ‘in her head or brain’, with its attendant problems for science.  She just sees a light in a room. Indeed, what the subject experiences is very similar to what the experimenter experiences when he gazes at the light (she just sees the light from a different angle) — in spite of the different terms they use to describe what they perceive (a ‘physical stimulus’ versus a ‘sensation of light’).  If so, there can be no actual difference in the ‘sub- jective’ versus ‘objective’ status of the light phenomenologically ‘experienced’ by S and ‘observed’ by E.  I have developed the case for this and analysed its consequences elsewhere (Velmans, 1993, 1996b, 2000b).  However, one can easily grasp the essential similarities between S’s ‘subjective experiences’ and E’s ‘objective observations’ from the fact that the roles of S and E are interchangeable.


A thought experiment: ‘changing places’

What makes one human being a ‘subject’ and another an ‘experimenter’? Their different roles are defined largely by differences in their interests in the experiment, reflected in differences in what they are required to do. The subject is required to focus only on her own experiences (of the light), which she needs to respond to or report on in an appropriate way.  The experimenter is interested primarily in the subject’s experiences, and in how these depend on the light stimulus or brain states that he can observe.

To exchange roles, S and E merely have to turn their heads, so that E focuses exclusively on the light and describes what he experiences, while S focuses her attention not just on the light (which she now thinks of as a ‘stimulus’) but also on events she can observe in E’s brain, and on E’s reports of what he experiences.  In this situation, E becomes the ‘subject’ and S becomes the ‘experimenter’.  Following current conventions, S would now be entitled to think of her observations (of the light and E’s brain) as ‘public and objective’ and to regard E’s experiences of the light as ‘private and subjective’.

However, this outcome is absurd, as the phenomenology of the light remains the same, viewed from the perspective of either S or E, whether it is thought of as an ‘observed stimulus’ or as an ‘experience’.  Nothing has changed in the character of the light that E and S can observe other than the focus of their interest. That is, in terms of phenomenology there is no difference between ‘observed phenomena’ and ‘experiences’. This raises a fundamental question: If the phenomenology of the light remains the same whether it is thought of a ‘physical stimulus’ or an ‘experience’, is the phenomenon private and subjective or is it  public and objective?

All experiences are private and subjective.

I do not have direct access to your experiences and you do not have direct access to mine.  For example I cannot experience your pain, your thoughts, your colour qualia, the way your body feels to you, the way the sky looks to you, the way I look to you, and so on. I can only have my own experiences (however well I empathise). The privacy and subjectivity of each individual’s experience is well accepted in philosophy of mind.  It seems to be a  fundamental given of how we are situated in the world.

In dualism, ‘experiences’ are private and subjective, while ‘physical phenomena’ are public and objective as noted above.  However, according to the reflexive model there is no phenomenal difference between physical phenomena and our experiences of them.  When we turn our attention to the external world, physical phenomena just are what we experience.  If so, there is a sense in which physical phenomena are ‘private and subjective’ just like the other things we experience.  For example, I cannot experience your phenomenal mountain or your phenomenal tree. I only have access to my own phenomenal mountain and tree. Similarly, I only have access to my own phenomenal light stimulus and my own observations of its physical properties (in terms of meter readings of its intensity, frequency, and so on).  That is, we each live in our own private, phenomenal world.  Few, I suspect, would disagree.

Public access to observed entities and events; public phenomena in the sense of similar, shared, private experiences.

If we each live in our own private, phenomenal world then each ‘observation’ is, in a sense, private. This was evident to the father of operationalism, the physicist P.W. Bridgman (1936), who concluded that, in the final analysis,  ‘science is only my private science’. However, this is clearly not the whole story.  When an entity or event is placed beyond the body surface (as the entities and events studied by physics usually are) it can be perceived by any member of the public suitably located in space and time.  Under these circumstances such entities or events are ‘public’ in the sense that there is public access to the observed entity or event itself.

This distinction between the phenomena perceived by any given observer and the entity or event itself is important. In the reflexive model, perceived phenomena represent things-themselves, but are not identical to them.  The light perceived by E and S, for example, can be described in terms of its perceived brightness and colour.  But, in terms of physics, the stimulus is better described as electromagnetism with a given mix of energies and  frequencies.  As with all visually observed phenomena, the phenomenal light only becomes a phenomenal light once the stimulus interacts with an appropriately structured visual system — and the result of this observed–observer interaction is a light as-experienced which is private to the observer in the way described above.  However, if the stimulus itself is beyond the body surface and has an independent existence, it remains there to be observed whether it is observed (at a given moment) or not.  That is why the stimulus itself is publicly accessible in spite of the fact that each observation/experience of it is private to a given observer.

To the extent that observed entities and events are subject to similar perceptual and cognitive processing in different human beings, it is also reasonable to assume a degree of commonality in the way such things are experienced.  While each experience remains private, it may be a private experience that others share. For example, unless observers are suffering from red/green colour blindness, we normally take it for granted that they perceive electromagnetic stimuli with wavelength of 700 nanometers as red and those of 500 nanometers as green.  Given the privacy of light phenomenology there is no way to be certain that others experience ‘red’ and ‘green’ as we do ourselves (the classical problem of the inverted spectrum and ‘other minds’).  But in normal life, and in the practice of science, we adopt the working assumption that the same stimulus, observed by similar observers, will produce similar observations or experiences.  Thus, while experienced entities and events (phenomena) remain private to each observer, if their perceptual, cognitive and other observing apparatus is similar, we assume that their experiences (of a given stimulus) are similar.  Consequently, experienced phenomena may be ‘public’ in the special sense that other observers have similar or shared experiences.

Being clear about what is private and what is public

From subjectivity to intersubjectivity

This re-analysis of private versus public phenomena also provides a natural way to think about the relation between subjectivity and intersubjectivity. Each (private) observation or experience is necessarily subjective, in that it is always the observation or experience of a given observer, viewed and described from his or her individual perspective.  However, once that experience is shared with another observer it can become inter-subjective.  That is, through the sharing of a similar experience, subjective views and descriptions of that experience potentially converge, enabling intersubjective agreement about what has been experienced.

How different observers establish intersubjectivity through negotiating agreed descriptions of shared experiences is a complex process that we do not need to examine here.  Suffice it to say that it involves far more than shared experience. One also needs a shared language, shared cognitive structures, a shared world-view or scientific paradigm, shared training and expertise and so on.  To the extent that an experience or observation can be generally shared (by a community of observers), it can form part of the data base of a communal science.

Different meanings of the term ‘objective’ that are used in science

According to the analysis above, phenomena in science can be ‘objective’ in the sense of intersubjective.  Note, however, that intersubjectivity requires the presence of subjectivity rather than its absence. Observation statements (descriptions of observations) can also be  ‘objective’ in the sense of being dispassionate, accurate, truthful, and so on.  Scientific method can also be ‘objective’ in the sense that it follows well-specified, repeatable procedures (perhaps using standard measuring instruments).  However, if the above analysis is correct, one cannot make observations without engaging the experiences and cognitions of a conscious subject (unobserved meter readings are not ‘observations’).  If so, science cannot be ‘objective’ in the sense of being observer-free.

Intra-subjective and inter-subjective repeatability

According to the reflexive model, there is no phenomenal difference between observations and experiences.  Each observation results from an interaction of an observer with an observed. Consequently, each observation is observer-dependent and unique. This applies even to observations made by the same observer, of the same entity or event, under the same observation conditions, at different times — although, under these circumstances, the observer may have no doubt that he/she is making repeated observations of the same entity or event.

If the conditions of observation are sufficiently standardised an observation may be repeatable within a community of (suitably trained) observers, in which case intersubjectivity can be established by collective agreement.  Once again, though, it is important to note that different observers cannot have an identical experience.  Even if they observe the same event, at the same location, at the same time, they each have their own, unique experience.  Intersubjective repeatability resembles intrasubjective repeatability in that it merely requires observations to be sufficiently similar to be taken for ‘tokens’ of the same ‘type’. This applies particularly to observations in science, where repeatability typically requires intersubjective agreement amongst scientists observing similar events at different times and in different geographical locations.

Consequences of the above analysis for a science of consciousness

The above provides an account of the empirical method — i.e. of what scientists actually do when they test their theories, establish intersubjectivity, repeatability and so on — which accepts that observed, physical phenomena just are the entities and events that scientists experience. Although I have focused on physical events, this analysis applies also to the investigation of events that are usually thought of as ‘mental’ or ‘psychological’. Although the methodologies appropriate to the study of physical and mental phenomena may be very different, the same epistemic criteria can be applied to their scientific investigation. Physical phenomena and mental (psychological) phenomena are just different kinds of phenomena which observers experience (whether they are experimenters or subjects). S1 to n  might, for example, all report that a given increase in light intensity produces a just noticeable difference in brightness, an experience/observation that is intersubjective and repeatable.  Alternatively, S1 to n  might all report that a given anaesthetic removes pain or, if they stare at a red light spot, that a green after-image appears, making such phenomena similarly public, intersubjective, and repeatable.

See Graphic.

This epistemic closure of psychological with physical phenomena is self-evident in situations where the same phenomenon can be thought of as either ‘physical’ or ‘psychological’ depending on one’s interest in it. At first glance, for example, a visual illusion of the kind  shown in Figure 3, might seem to present difficulties, for the reason that physical and psychological descriptions of this phenomenon conflict.

Physically, the figure consists entirely of squares, joined in straight lines, while subjectively, most of the central lines in the figure seem to be bent. However, the physical and psychological descriptions result from two different observation procedures. To obtain the physical description, an experimenter E typically places a straight edge against each line, thereby obscuring the cues responsible for the illusion and providing a fixed reference against which the curvature of each line can be judged. To confirm that the lines are actually straight, other experimenters (E1 to  n) can repeat this procedure. In so far as they each observe the line to be straight under these conditions, their observations are public, intersubjective and repeatable.

But, the fact that the lines appear to be bent (once the straight edge is removed) is similarly public, intersubjective and repeatable (amongst subjects S1 to n). Consequently, the illusion can be investigated using relatively conventional scientific procedures, in spite of the fact that the illusion is unambiguously mental.  One can, for example, simply move the straight edge outside the figure making it seem parallel to the bent central lines — thereby obtaining a measure of the angle of the illusion.

The empirical method

In short, once the empirical method is stripped of its dualist trappings, it applies as much to the science of consciousness as it does to the science of physics in that it adheres to one, fundamental principle.  Stated formally:

If observers E1 to n (or subjects S1 to n), carry out procedures P1 to n, under
observation conditions O1 to n, they should observe (or experience) result R

(assuming that E1 to n and S1 to n have similar perceptual and cognitive systems, that P1 to n are the procedures which specify the nature of  the experiment or investigation, and that O1 to n includes all relevant background conditions, including those internal to the observer, such as their attentiveness, the paradigm within which they are trained to make observations and so on).

Put informally, empirical investigation of external or inner events is simply this:

If you carry out these procedures you will observe or experience these results.


Bridgman, P.W. (1936), The Nature of Physical Theory (Princeton, NJ: Princeton University Press).

Cohen, J.D. and Schooler, J.W. (ed. 1997), Scientific Approaches to Consciousness (Hillsdale, NJ: Lawrence Erlbaum).

Velmans, M. (1993), ‘A reflexive science of consciousness’, in Experimental and Theoretical Studies of Consciousness. CIBA Foundation Symposium 174 (Chichester: Wiley).

Velmans, M. (ed. 1996a), The Science of Consciousness: Psychological, Neuropsychological and Clinical Reviews (London: Routledge).

Velmans, M. (1996b), ‘What and where are conscious experiences?’, in The Science of Consciousness: Psychological, Neuropsychological and Clinical Reviews, ed. M. Velmans (London: Routledge).

Velmans, M. (ed. 2000a), Investigating Phenomenal Consciousness: New Methodologies and Maps (Amsterdam: John Benjamins, forthcoming).

Velmans, M. (2000b), Understanding Consciousness (London: Routledge, in press).