Readings Index


If Two Minds Are Better Than One, Then How About Two Thousand?

 A Review of Marvin Minsky's The Society of Mind

Every once in a while, one encounters a book so strikingly fertile and original that after reading it, one can never be quite the same. Its ideas resonate, sounding depths in one’s everyday life, clarifying what was previously obscure and raising questions that one never even knew existed. Such a book is Marvin Minsky’s The Society of Mind. In this book, Minsky, arguably  the foremost researcher in the field of artificial intelligence, shares with lay audiences ideas developed through many decades of careful thinking about how minds, natural and artificial, might work. The late Carl Sagan, a friend of Minsky’s, often lamented the fact that first-rate scientists rarely condescend to explain their work to nonspecialists. We can be greatful that Minsky saw the value in letting those of us who are not specialists in AI and robotics have a glimpse of his work. 

The cornerstone of  Minsky’s theory is the conception of minds as collections of enormous numbers of semi-autonomous, intricately connected agents that are themselves mindless.  As Minsky puts it, 

    This book tries to explain how minds work. How can intelligence emerge from nonintelligence? To answer that, we’ll show that you can build a mind from many little parts, each mindless by itself. 

    I’ll call “Society of Mind” this scheme in which each mind is made of many smaller processes. These we’ll call agents. Each mental agent by itself can only do some simple thing that needs no mind or thought at all. Yet when we join these agents in societies—in certain very special ways—this leads to intelligence. (17)

Just as the mind, according to Minsky, is made up of many tiny agents, so Minsky’s book is made up of many tiny, interrelated chapters. A typical chapter begins by describing a phenomenon, such as young children’s tendency to draw people as circular heads from which sticklike arms and legs protrude. The chapter then explains, generally, an internal mechanism that might account for such a phenomenon: 
    We’ll suppose that the child does not have anything like a picture in mind, but only some network of relationships that various “features” must satisfy. For example, a child’s “person-drawing” feature-network might consist of the following features and relations: 
       HEAD Large closed figure. 
       EYES Two circles, high in head. 
       MOUTH Object centered below eyes. 
       BODY Large closed figure. 
       ARMS Two lines, attached high on body. 
       LEGS Two lines, attached low on body. 
    To convert this description into an actual drawing, the child must employ some sort of “drawing procedure.” Here’s one in which the process simply works its way down the feature list, like a little computer program: 
      1. Consider the next feature on this list. 
      2. IF such a feature is already drawn, go to step 3. Otherwise draw it. 
      3. IF list is finished, stop. Otherwise, go back to step 1. 
    When the child starts to draw, the first item on the list is “large closed figure.” Sincere there isn’t any such thing yet, the child draws one: that’s the head. Next the eyes and mouth get drawn. But then, when it comes to drawing the body feature, step 2 of the procedure finds that a “large closed figure” has already been drawn. Accordingly, nothing new is required, and the procedure simply advances to step 3. (135)
This explanation of children’s drawings is typical of the kind to be found in Minsky’s book. The explanation is not meant to be a final, definitive statement about what actually happens in the brain but rather shows how one might explain the phenomenon from an engineering point of view. As one might expect of a man who pioneered AI and made seminal contributions to robotics, Minsky looks at a mental phenomenon and then asks himself what sort of mechanisms in the mind could account for it. 

Minsky is at pains to point out that much of what we take for granted is really incredibly complex. Early AI researchers soon learned that it was far easier to model on computers the kind of sophisticated, conscious knowledge that experts have in a given field than it is to model simple, largely unconscious abilities that we take for granted, such as remembering how to get to our homes, balancing ourselves on a bicycle, recognizing a parent’s face, or using language. As Minsky puts it, “Easy things are hard.(29)” Minsky points out that in the 1960s, he and Seymour Papert spent several years developing a program that would have the ability to build towers out of blocks. Such a Builder agent is itself made up of subagents such as Begin, Add, and End. Add is made up of the subagents Find, Get, and Put. Get is made up of the subagents Grasp and Move. All these mindless agents are connected in bureaucracies, in which agents report to other agents, and most of this work occurs below the level of consciousness, which is why it is so difficult to think clearly about them. As Minsky puts it, 

    Consider just the seemingly simple problem of not reusing blocks already built into the tower. To a person, this seems simple common sense: “Don’t use an object to satisfy a new goal if that object is already involved in accomplishing a prior goal.” No one knows exactly how human minds do this. Clearly we learn from experience to recognize the situations in which difficulties are likely to occur, and when we’re older we learn to plan ahead to avoid such conflicts.  But since we cannot be sure what will work, we must learn policies for dealing with uncertainty. Which strategies are best to try, and which will avoid the worst mistakes? Thousands and, perhaps, millions of little processes must be involved in how we anticipate, imagine, plan, predict, and prevent—and yet all this proceeds so automatically that we regard it as “ordinary common sense.” But if thinking is so complicated, what makes it seem so simple? At first it may seem incredible that our minds could use such intricate machinery and yet be unaware of it. 

    In general, we’re least aware of what our minds do best. (29)

In the course of his book, Minsky addresses many fascinating questions in light of his Society of Mind theory. He does an admirable job of exlaining how collections of mindless mechanisms could account for phenomena as diverse as memory, learning, jokes, fashions, self-images, intentions, classification, apprehension of analogies and metaphors, the difference between seeing and remembering, motivation, fantasizing, stages of development, commonsense versus logical reasoning, autism, the formation of identity in spite of our underlying multiplicity, and the “necessary illusion” of free will. Minsky is adamant that all events are, at base, physical phenomena and are either caused or occur by chance. In Minsky’s view, people are extremely complex machines, though Minsky would argue that when we use the word machine, we tend to think, erroneously, of very simple machines that “behave only in lifeless, mechanical ways” rather than in terms of machines as complex as the human brain, with its “billions of cells, each one complicated by itself and connected to many thousands of others” (30). To make his point about brains as machines, Minsky asks us to imagine replacing each cell in a brain with a computer chip designed to perform the same functions and connected to the other chips exactly as the brain cells are connected. According to Minsky, “There isn’t any reason to doubt that the substitute machine would think and feel the same kinds of thoughts and feelings that you do—since it embodies all the same processes and memories. Indeed, it would surely be disposed to declare, with all your own intensity, that it is you” (289). 

At one point in this fascinating, accessible, yet challenging book, Minsky quotes Wolfgang Pauli as saying, “That theory is worthless. It isn’t even wrong!” Minsky would be the first to admit that many parts of his theory are highly speculative. Even where Minsky’s ideas prove, one day, to have been wrong, they will have yielded powerful results, providing us with ways to begin thinking clearly about who we are and how we work. Minsky has spent his life in a demanding field in which a theory of a process is as good as the program that one can write or the robot that one can build to instantiate it. Time and time again, in reading Minsky, one has the satisfying feeling that one has when assembling a complicated appliance and having it operate smoothly. Ah, yes, that works. And even when it doesn’t work, by actually attempting to build the machine that instantiates the theory, we can learn what parts don’t operate and begin to conceptualize alternatives. One of the reasons why artificial intelligence is important is that it provides a testing ground for psychological theorizing, forcing theorists to make their thinking concrete and operational. Minsky’s book is an example of operational thinking at its best and will doubtless serve as a roadmap for much of the work in artificial intelligence and cognitive psychology in years to come. 


Minsky, Marvin. The Society of Mind. New York: Simon and Schuster, 1986. 

Minsky, Marvin. The Society of Mind CD-ROM, Macintosh Version. New York: Learn Technologies Interactive, 1996. 

Minsky, Marvin. The Society of Mind CD-ROM, Windows Version. New York: Learn Technologies Interactive, 1997. 

Questions for Discussion and Review 

The following questions are based on the preceding text. Clicking on a question will take you to the place in the text where the question is discussed. To return to these questions, simply click the "Back" button in your browser. 

1. What does Marvin Minsky call his theory of mind, and what is its central idea? 

2. How does Minsky explain those drawings of people made by children in which arms and legs are directly attached to large, circular heads? 

3. What role do concepts from engineering play in Minsky's explanations of human abilities and mental phenomena? 

4. What surprising fact did early AI researchers learn about so-called "easy abilities" such as balancing on a bicycle or learning to speak? 

5. According to Minsky, what are we least aware of? 

6. What are some of the phenomena that Minsky explains in his book? 

7. What thought experiment does Minsky propose to support his contention that the brain is a complex machine? 

8. Why is research into artificial intelligence important for progress in the field of psychology? 


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