Pat Gunning writes:  
"... to define anything, we must   
imagine the thing without one or more of the attributes that we employ   
in our definition. What we imagine is, to Mises, an imaginary   
construction. This is all that Mises means by an imaginary construction.   
It is also what he has in mind when he says that economics and   
praxeology cannot do without imaginary constructions. He applies this   
general idea to what he calls praxeological phenomena -- phenomena   
related to what he calls action. The method of imaginary constructions   
is a means of reaching an understanding of a specific case of economic   
interaction by conceiving of the interaction in the absence of some   
characteristic that we use to define it."  
  
  
Whew.  
  
To the extent I understand the above, it was effectively opposed by Francis  
Bacon, in Novum Organum, who wrote:  
  
 "Man ... can understand ... so much only as he has observed ... of the  
course of nature."  
  
 "One method of delivery (from error) alone remains to us; which is simply  
this: we must lead men to the particulars themselves; and their series and  
order; while men on their side must force themselves for awhile to lay their  
notions by and begin to familiarize themselves with facts."  
  
Many regard Bacon's attitude as a vital ingredient in the progress of  
science.  
  
Thus Milton Friedman became viewed as outstanding not mainly by recycling  
ancient views from Nassau Senior et al., but by persuading people (with a  
little help from Anna Schwartz) that the Great Depression did not spring  
from endogenous faults of the market economy. He did this by documenting  
blundering and bad timing by leaders of the Federal Reserve System, which  
could be seen as exogenous. I disagree, but that means nothing when so many  
powerful and heavily subsidized pundits seized on his views. And so it came  
to pass that the recycled prejudices of Nassau Senior et al. came to be  
labeled as "monetarism", and imposed on much of the world. As we work out  
from under this handicap, which now has alienated much of the world, we  
would do well to focus on facts.  
  
Mason Gaffney