I know this is open ended but what do Karl Marx, Adam Smith, Shumpeter, and Keynes have in common in terms of thinking. I am studying them right now and my prof. says that they are the grandmasters of political economy. I understand their role with capitalism and how after smith, they thought capitalism would fall and turn into socialism or communism. Do you know any modern examples of their theories in the works. thanks

Question

First off, neither Shumpeter or Keynes thought capitalism would "fall". Although, as I recall, both wrote about problems with capitalism.
That said, all of these "grandmasters" have produced ideas that are still accepted and taught and used today. "Tax Cuts to stimulate the economy" is a page right out of Keynes. Advantages from specialization and trade is something Smith taught over 200 years ago. Today's concepts of inovation and entrepreneurs can be traced by to Shumpeter. Modern ideas of social class have roots in the writings of Karl Marx.