Short answers, pulled from the story.
Lionel Robbins released his Essay on the Nature and Significance of Economic Science in London during 1932. Macmillan published this first edition, setting the stage for academic debate across Europe and North America.
Robbins defined economics as the science which studies human behaviour as a relationship between ends and scarce means which have alternative uses. He argued that wealth is not wealth because of its substantial properties but because it is scarce.
The Essay separated ascertainable facts of positive theory from normative judgments on economic policy. Robbins insisted that economics deals with what can be observed rather than what ought to be done.
Peter Groenwegen noted this shift destroyed the view classical economists had of their science. The work generated tightly argued radical implications from a simple definition regarding scarcity.
By 1960 the text stood as a foundational methodology text for generations of scholars. Arguments therein were widely accepted on the demarcation of economics as science from discussion of recommendations on economic policy.