I would like to revive an old idea about the mind. This is the idea that the mind arises from, and is principally about, our sensori-motor interaction with the world. It is the idea that all our sense of the world, of space, objects, and other people, arises from our experience squeezed through the narrow channel of our sensation and action. This is a radical view, but in many ways an appealing one. It is radical because it says that experience is the only thing that we directly know, that all our sense of the material world is constructed to better explain our subjective experience. It is not just that the mental is made primary and held above the physical, but that the subjective is raised over the objective.
Subjectivity is the most distinctive aspect of this view of the mind, and inherent in it. If all of our understanding of the world arises from our experience, then it is inherently personal and specific to us.
As scientists and observers we are accustomed to praising the objective and denigrating the subjective, so reversing this customary assessment requires some defense.
The approach that I am advocating might be termed the subjective viewpoint. In it, all knowledge and understanding arises out of an individual's experience, and in that sense is inherently in terms that are private, personal, and subjective. An individual might know, for example, that a certain action tends to be followed by a certain sensation, or that one sensation invariably follows another. But these are its sensations and its actions. There is no necessary relationship between them and the sensations and actions of another individual. To hypothesize such a link might be useful, but always secondary to the subjective experience itself.
The subjective view of knowledge and understanding might be constrasted with the objective, realist view. In this view there are such things as matter, physical objects, space and time, other people, etc. Things happen, and causally interact, largely independent of observers. Occasionally we experience something subjectively, but later determine that it did not really, objectively happen. For example, we felt the room get hot, but the thermometer registered no change. In this view there is a reality independent of our experience. This would be easy to deny if there were only one agent in the world. In that case it is clear that that agent is merely inventing things to explain its experience. The objective view gains much of its force because it can be shared by different people. In science, this is almost the definition of the subjective/objective distinction: that which is private to one person is subjective whereas that which can be observed by many, and replicated by others, is objective.
I hasten to say that the subjective view does not deny the existence of the physical world. The conventional physical world is still the best hypothesis for explaining our subjective data. It is just that that world is held as secondary to the data that it is used to explain. And a little more: it is that the physical world hypothesis is just that, a hypothesis, an explanation. There are not two kinds of things, the mental and the physical. There are just mental things: the data of subjective experience and hypotheses constructed to explain it.
The appeal of the subjective view is that it is grounded. Subjective experience can be viewed as data in need of explanation. There is a sense in which only the subjective is clear and unambiguous. "Whatever it means, I definitely felt warm in that room." No one can argue with our subjective experience, only with its explanation and relationship to other experiences that we have or might have. The closer the subjective is inspected, the firmer and less interpreted it appears, the more is becomes like data, whereas the objective often becomes vaguer and more complex. Consider the old saw about the person who saw red whenever everybody else saw green, and vice versa, but didn't realize it because he used the words "red" and "green" the wrong way around as well. This nonsense points out that different people's subjective experiences are not comparable. The experience that I call seeing red and the experience you call seeing red are related only in a very complicated way including, for example, effects of lighting, reflectance, viewpoint, and colored glasses. We have learned to use the same word to capture an important aspect of our separate experience, but ultimately the objective must bow to the subjective.
The appeal of the objective view is that it is common across people. Something is objectively true if it predicts the outcome of experiments that you and I both can do and get the same answer. But how is this sensible? How can we get the same answer when you see with your eyes and I with mine? For that matter, how can we do the "same" experiment? All these are problematic and require extensive theories about what is the same and what is different. In particular, they require calibration of our senses with each other. It is not just a question of us using the same words for the same things -- the red/green example shows the folly of that kind of thinking -- it is that there is no satisfactory notion of same things, across individuals, at the level of experience. Subjective experience as the ultimate data is clear, but not the idea that it can be objectively compared across persons. That idea can be made to work, approximately, but should be seen as following from the primacy of subjective experience.
At this point, you are probably wondering why I am belaboring this philosophical point. The reason is that the issue comes up, again and again, that it is difficult to avoid the pitfalls associated with the objective view without explicitly identifying them. This fate has befallen AI researchers many times in the past. So let us close with as clear a statement as we can of the implications of the subjective view for approaches to AI. What must be avoided, and what sought, in developing a subjective view of knowledge and mind?
All knowledge must be expressed in terms that are ultimately subjective, that are expressed in terms of the data of experience, of sensation and action. Thus we seek ways of clearly expressing all kinds of human knowledge in subjective terms. This is a program usually associated with the term "associationism" and often denigrated. Perhaps it is impossible, but it should be tried, and it is difficult to disprove, like a null hypothesis. In addition to expressing knowledge subjectively, we should also look to ways of learning and working with subjective knowledge. How can we reason with subjective knowledge to obtain more knowledge? How can it be tested, verified, and learned? How can goals be expressed in subjective terms?