The U.S. Department of Energy employs physics Ph.D.s to manage our nuclear weapons. How would you feel if some of them wrote blog posts saying that it is possible to build a perpetual motion machine? What if they did this to signal their loyalty to some club of physicists? Wouldn’t you wonder why membership in this club was important enough get them say that they do not believe the second law of thermodynamics?

Lucas (2009) makes a misleading claim about models of growth: S1: {adding books} => {no change in growth} David Andolfatto admits that S1 is false and the true statement is {adding books} => {{no change in growth} or {sustained change in growth}}. But he professes not to see why anyone should care that Lucas engages in this type of mathiness; that is, why anyone should care that Lucas makes a misleading verbal statement about the mathematics of growth theory.

The key to understanding mathiness is to recognize how a formal language can interact with natural language. The source code for a computer program has formal statements written in a language like C that will be interpreted by a compiler. It will also have comments and messages written in natural language that will be read by a person. Compared to mathematics, source code is easy to analyze because the statements in the two languages are kept separate.

After more than 100 years of incremental change, urban transportation is on the verge of a revolution. Last week, NYU’s Alain Bertaud brought together a small group with backgrounds that included transportation engineering, urban planning, economics, and applied physics, and who worked in the private sector, universities, think tanks, or government agencies in US, China, South Korea, and India to compare notes on what they are seeing. It soon became clear that our familiar words were getting in the way.

Dietz Vollrath has a new post that continues the discussion about how economists use math. He makes an important point (see #4 below) that I’ve tried to capture in the title and has also spurred a few other thoughts. DV: Romer’s motivation is irrelevant I agree with Dietz on this point. The attempts at starting a discussion about whether I am a bad person, and what sound like follow-on attempts at starting a discussion about whether Dietz is a bad person, need to be understood as evidence that the problems in the papers I criticize are real.