SUPPLY AND DEMAND 
73 
ruination of the results of such efforts, nature 
plays a predominant part, and the best and 
most conveniently situated natural resources 
are strictly limited in quantity. 
It is hardly needful to say that the realistic 
laws of returns and the abstract laws of returns 
supplement one another. They both relate 
to the same facts, broadly speaking; but 
while the realistic laws have a more practical 
value in adding directly to our information 
about economic affairs, as the latter imme 
diately present themselves to us, it is the 
abstract laws which have the greater specula 
tive value in satisfying our minds as to the 
causes of things. One defect of the realistic 
laws is that they cannot be universally 
affirmed. We have to introduce such qualify 
ing phrases as “usually” or “generally.” 
The abstract laws attain absolute universality, 
but only at the sacrifice of immediate applica 
bility. 
All this is a digression, though a necessary 
digression. We may now pick up the main 
thread of our argument, and at once hasten to 
unite it with our earlier exposition of demand. 
The supplies of reproducible things we have 
seen depending upon ruling prices. When 
constant returns is found there is one supply