See Hudson's January 2004 paper, "The Mathematical Economics of  
Compound Rates of Interest: A Four-Thousand Year Overview, Part I"

Four-fifths of the way through the paper is a section titled  
"Economics vs. the Natural Sciences: The airy methodology of 'as if'  
" which begins:
> What is even more remarkable is the idea that economic assumptions  
> need not have any relationship to reality at all. This attitude is  
> largely responsible for having turned economics into a mock- 
> science, and explains its rather odd use of mathematics.
>

In it, Hudson writes, quoting Mill:

> The sophistical tendency can be traced back to John Stuart Mill?s  
> 1844 essay ?On the Definition of Political Economy; and on the  
> Method of Investigation Proper to it?:
>
>             In the definition which we have attempted to frame of  
> the science of Political Economy, we have characterized it as  
> essentially an abstract science, and its method as the method a  
> priori. . . . Political Economy, therefore, reasons from assumed  
> premises ? from premises which might be totally without foundation  
> in fact, and which are not pretended to be universally in  
> accordance with it. The conclusions of Political Economy,  
> consequently, like those of geometry, are only true, as the common  
> phrase is, in the abstract; that is, they are only true under  
> certain suppositions, in which none but general causes ? causes  
> common to the whole class of cases under consideration ? are taken  
> into account.
>


Hudson's paper was the fifth hit on a google search for "Michael  
Hudson John Stuart Mill". It is online at http://www.michael- 
hudson.com/articles/debt/CompoundInterest1.html .

Pat Inman