Price rigidity and market-clearing: a conceptual clarification

This article tests the view (derived from Hicks and Patinkin)that non-market clearance may be caused by slow adjustment (‘processrigidity’). There are models where market-rationing ispresent and derives from some form of rigidity, but this rigiditycannot be considered as process rigidity. It is similarly possibleto accommodate the idea of process rigidity within the Marshallianresearch programme. What is missing is that market-rationingmight be its corollary. The reason such a causal link is oftenbelieved to exist lies in a generic use of the concept of rigidity,used to designate alternative and incompatible phenomena: ‘exogenousend-state rigidity’ and ‘equilibrium end-state rigidity’,as well as process rigidity. It is true that these first twoforms of rigidity create market rationing. The belief that slowadjustment also generates market rationing results from theunwarranted extension to process rigidity of conclusions whichare only valid for the first two.