Mental Models

Although it is perhaps self-evident that humans regularly create and use formal models, it is less obvious that they regularly create and use informal models, or mental models. More precisely, human beings do not have actual families, clubs, churches, universities, corporations, cities, states, national socioeconomic systems, and the like, inside of their heads, but rather mental representations of these systems. Thus, in the field of system dynamics it is argued that policy makers should not worry about whether or not to use a model, but rather which model to use. In other words, system dynamicists believe that policy makers should decide whether they wish to make decisions based on results obtained from their unaided mental models, or from results obtained from some combination of formal and mental models.

Both formal models and mental models have many strengths and weaknesses. Mental models are flexible, rich in detail, and constructed from the most abundant and valuable source of information in the world - experience "data" collected in your brain. John Sterman, a prominent system dynamics professor at Massachusetts Institute of Technology, points out that the "great systems of philosophy, politics, and literature are, in a sense, mental models".

To illustrate the importance of mental models, it is useful to consider the following thought experiment . Imagine that spacemen land in Detroit, remove every worker from one of the city's automobile plants, and replace them with workers who are identical in every way to the removed workers, except that they have no mental information to guide them in making automobiles. Could the new workers build automobiles by using the available written and numerical information? The answer is "no," and the reason is that an overwhelming majority of the information that is crucial for automobile manufacturing is contained in the minds of the removed workers.

Although mental models have many strengths, they also have many weaknesses. Mental models are often fuzzy, incomplete, imprecise, and filled with unstated assumptions and goals. During conversation and debate, different people use different mental models, and these models can and do change -- even during the course of a single conversation or debate. Further, the human mind is a poor dynamic simulator. Cognitive limitations prevent humans from accurately thinking through the dynamic behavior inherent in all but the simplest of their mental models.

To illustrate the richness and complexity of human mental models and the difficulty of thinking through their dynamic consequences, it is useful to examine Douglas Hofstadter's book Gödel, Escher, Bach: An Eternal Golden Braid . In his book, Hofstadter integrates Gödel's Incompleteness Theorem, the music of Johann Sebastian Bach, and the art of Maurits Cornelis Escher, to address the issue of whether machine reasoning and artificial intelligence are truly possible. Hofstadter's self-made sketch of a portion of his mental model that underlies his book is presented in Figure 1.

(click on image to see detailed view)

Figure 1: Hofstadter's self-made sketch of a portion of his mental model

After examining Hofstadter's sketch, it is perhaps easier to accept the argument that trying to accurately think through the dynamic behavior inherent in mental models is a difficult task indeed!