Regarding "Economics is the science of choice":   
  
I think an important phrase has been left out - Economics is the science   
of choice _under conditions of scarcity_. Scarcity is what gives rise to   
the notions of opportunity cost, of economizing activity and the related   
notion of economic value, and of gains from trade. Lionel Robbins defended   
this in The Nature and Significance of Economic Science; and before him   
Wicksteed. The Austrians had a similar view.   
  
One may dispute whether this captures economics (it misses empirical   
studies of all sorts, for example)  but if one is going to defend it as a   
definition, the additional phrase "in a world of scarcity" seems to me to   
be a necessary component.   
  
Bruce Caldwell