And the reason is a very simple one: Fisher has followed the quantity theory to its logical conclusions!
Certainly in its origin, the quantity theory is much the older theory.
A reasonable interpretation of the quantity theory makes it a statement of the effect of a change in a single factor.
It is a part of the quantity theory that this is unnecessary.
Well, viewed merely as a matter of mechanical equilibration, the quantity theory view is not strictly true, by any means.
There is no such a priori simplicity as the quantity theory deals with.
The quantity theory explanation of international gold movements is as follows: if money comes into a country, it raises prices.
For the quantity theory, the fall will be in proportion to the increase.
In the cases where they conflict, the first named doctrines are correct, and the quantity theory is wrong.
The quantity theory has no explanation of elasticity to give.