John Maynard Keynes is considered a foundational source in the understanding of macroeconomics.

 John Maynard Keynes is considered a foundational source in the understanding of macroeconomics. After performing research outside the textbook, please explain in three well-structured paragraphs the basic principles of the New Keynesian Economics and how it addresses perceived limitations to classic Keynesian theory.

Please mention the sources and references.

Thanks.