This paper is concerned with the practical problems associated with un
derstanding and defining the concept of simplicity. Different attempts
that have been made to define simplicity and, in particular, definiti
ons based on counting parameters, are discussed and analyzed. The limi
tations of these attempts, especially as applied to economics, are ill
ustrated by means of several econometric examples, including single-eq
uation models, systems of equations, alternative functional forms, and
probability distributions.