← Thinking in Loops · Lesson 4 of 4
Every model is an argument
In 1969 Jay Forrester published Urban Dynamics, a computer model of a city. It concluded that building low-cost housing could make a city worse off, by drawing in people faster than jobs. The book was controversial then and is argued about now.
Twenty years later the game SimCity drew on the same kind of thinking. Its cities obey rules someone chose: how far people will travel to work, what makes them move away. Play enough and you are learning those rules, not a fact about real cities.
That is true of every model, including the small ones in this course. A model is a careful argument: if these premises hold, then this follows. The useful question is never only "what does it say?" but "what would have to be true for it to be right?"
Two towns, one argument
Out of work, building homes: starts at 40, ends at 296, highest 296. Out of work, building workplaces: starts at 40, ends at 0, highest 40.
Try this: The model says building homes leaves more people out of work. Now slide the home pull all the way to 0: the gap closes. The conclusion was in that premise all along.
What this model assumes
- An empty home pulls people in about as hard as an open job does. (argued about)
- Six in ten residents look for work. (a guess)
- Nobody commutes in from outside the town. (a guess)
- Each town builds only one thing: the workplaces town adds no homes, so its population can hardly grow. (a guess)
A model says building more homes will raise unemployment in a town. What is the most useful first question to ask?