However, while factors other than money in the Equation of Exchange might affect the price level, thus qualifying the proposition of rigid proportionality, Fisher’s discussion implied that they were of secondary importance, for substantial changes in the price level, in his view, could only occur through a change in the money supply. Moreover, to the extent that interdependence exists between the variables in the equation of exchange, it will not be possible to assert that money is strictly neutral, and it may not be possible to assert the strict exogeneity of money. To the extent that interdependence is weak, money will be mostly neutral and mainly exogenous.