Science is often thought of as involving facts that are directly given to unprejudiced observers through their senses, facts that precede and are independent of theory, and facts that provide a firm basis for scientific knowledge. A.F. Chalmers argues against these widely accepted ideas.
It is widely believed that facts concerning the world around us come to us directly through the senses. This would lead us to believe that observing the world around us and recording what is seen or otherwise experienced through the senses is all there is to observation. In this way it is thought, what is seen is the way that things external to us really are. The sense impressions we have from objects are direct data concerning the true nature of the objects we are experiencing. The nature of whatever was being looked at would determine what it is we saw, and different people observing the same external objects would always see or otherwise experience the same thing. Chalmers advances an argument against this view.
Two normal observers viewing the same object from the same place under the same physical circumstances do not necessarily have identical visual experiences, even though the images on their respective retinas may be virtually identical. There is an important sense in which the two observers need not “see” the same thing. As N.R. Hanson (1958) has put it, “there is more to seeing than meets the eyeball”. (1)
As an example of this phenomenon Chalmers presents a picture which looks like a staircase, then an upside down staircase, then changes back and forth between the two. African cultures do not see a “staircase” at all since they have no concept of what a staircase is and furthermore are used to seeing things in two dimensions instead of three dimensions. Since the image itself is not undergoing any change and even is viewed by the same observer there is nothing in the image itself changing (or in the retinal image). A second example involves a children’s puzzle which is a picture of a tree with a face that is difficult to see at first. Once the face is detected it is easily seen each time the picture is viewed, yet the picture and even the viewer remain unchanged. Chalmers concludes from this that in some way what is seen by people is changed by past experience. These considerations are applicable to science as well.
In response, it is not difficult to produce examples from the practice of science that illustrate the same point, namely, that what observers see, the subjective experiences that they undergo, when viewing an object or scene is not determined solely by the images on their retinas but depends also on the experience, knowledge and expectations of the observer. The point is implicit in the uncontroversial realisation that one has to learn to be a competent observer in science. (2)
Experience, knowledge, and expectations affect what people see. This is the point of the examples provided by Chalmers and the point directly relevant to science because of the notion that observation in science requires some skill. For example, one generally learns how to look through a microscope and learns to be able to identify what one specifically is looking for in a slide or is looking at. At first, inexperience results in fewer discernible entities being seen by the observer. Again, the same thing may be viewed by the same observer, but it is affected by the factors that Chalmers identifies. The same thing occurs with students who are learning to read X-ray pictures.
The experienced and skilled observer does not have perceptual experiences identical to those of the untrained novice when the two confront the same situation. This clashes with a literal understanding of the claim that perceptions are given in a straightforward way via the senses. (3)
The objection to Chalmer’s understanding of perception is that what is different in observer’s experiences is only the interpretation of what is seen. What is seen, it is thought, is the same in the examples given, but the perceptions in each scenario are interpreted differently. For example, the African tribes simply do not interpret the illusion of the staircase as a staircase, even though they see the very same lines that anyone else does. The X-ray photos are the same when a student begins to learn to read them as they are later on after the student has learned to read them, and so the interpretation of the X-ray photos is what changes from one instance to the next. Chalmers disagrees with this idea though.
As far as perception is concerned, the only things with which an observer has direct and immediate contact are his or her experiences. These experiences are not uniquely given and unchanging but vary with the knowledge and expectations possessed by the observer. What is uniquely given by the physical situation, I am prepared to admit, is the image on the retina of an observer, but an observer does not have direct perceptual contact with that image. When defenders of the common view assume that there is something unique given to us in perception that can be interpreted in various ways, they are assuming without argument, and in spite of much evidence to the contrary, that the images on our retinas uniquely determine our perceptual experiences. They are taking the camera analogy too far. (4)
Chalmers does not dispute the claim that physical causes which bring about images on retinas have something to do with what is seen. He also does not mean to say that what is seen in various situations is not, to a large extent, stable. Observers who see something different in the same situation still in some sense are seeing the same thing. Chalmers also does not wish to dismiss that a physical world external to ourselves exists but does wish to argue that our perceptions of this single world differ significantly.
- A.F. Chalmers. What is this thing called Science? 3rd Edition. Hackett Publishing Company Inc. Indianapolis/Cambridge. 1999. Pg. 5.
- Ibid. Pg. 7.
- Ibid. Pg. 8.
- Ibid. Pg. 8-9.
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