Presidential Address: Mathematics in economics and econometrics

The paper discusses the choices of mathematical approaches in economics and econometrics, in particular, approaches that either (a) aim for a sharp result or (b) use the least restrictive assumptions. It is argued that, while the choice (a) often necessitates strong mathematical assumptions, choice (b) may lead to only partial identification and may require using less familiar mathematical techniques. This is discussed in the context of the problem of defining a probability density: existence may fail in function spaces; even after imposing assumptions that ensure existence, the problem is not well posed. A density function may not exist for economic variables as a consequence of institutional rigidity such as an income supplement. The apparatus of generalized functions provides the general solution to identification and well-posedness of density, but at the cost of less sharp results and greater mathematical complexity.