Two issues are discussed in this paper. The first is whether a formal
definition and justification of simplicity (parsimony) in scientific i
nference can be found, and whether an optimal level of simplicity is o
btainable. A definition of simplicity is possible, as are the optimum
conditions for the desired degree of simplicity. The model of inferenc
e used here relates Bayesian inference to algorithmic information theo
ry. Simplicity is examined in the light of induction, the Duhem-Quine
thesis, and bounded rationality. The second issue relates to the role
that simplicity might play in econometric modelling. This is elucidate
d with some remarks on the 'general to specific' approach to modelling
and discussion on the purpose of a model.